Bump actions/checkout from 3 to 6 (#174)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/docs.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
           fetch-depth: ${{ github.event_name != 'push' && 1 || 0 }}

.github/workflows/linux.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-24.04
     env: {CXXFLAGS: "-Werror -Wshadow -Woverloaded-virtual -Wunreachable-code -fno-operator-names"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies.sh
     - name: Build & Install
@@ -48,7 +48,7 @@ jobs:
     runs-on: ubuntu-24.04
     env: {CXXFLAGS: "-Werror -Wno-error=deprecated-declarations -Wshadow -Woverloaded-virtual -Wunreachable-code -fno-operator-names"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies.sh
     - name: Build & Install
@@ -78,7 +78,7 @@ jobs:
     runs-on: ubuntu-24.04
     env: {CXXFLAGS: "-Werror -Wshadow -Woverloaded-virtual -Wextra-semi -Wunreachable-code -fno-operator-names"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies_clang.sh 18
     - name: Build & Install
@@ -114,7 +114,7 @@ jobs:
     runs-on: ubuntu-24.04
     env: {CXXFLAGS: "-Werror -Wshadow -Woverloaded-virtual -Wunreachable-code -fno-operator-names"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies.sh
     - name: Build & Install
@@ -145,7 +145,7 @@ jobs:
     runs-on: ubuntu-24.04
     env: {CXXFLAGS: "-Werror -Wshadow -Woverloaded-virtual -Wunreachable-code -fno-operator-names"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies.sh
     - name: Build & Install
@@ -174,7 +174,7 @@ jobs:
     runs-on: ubuntu-24.04
     env: {CXXFLAGS: "-fno-operator-names"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies_nvcc.sh 12.6
     - name: Build & Install
@@ -206,7 +206,7 @@ jobs:
     runs-on: ubuntu-24.04
     env: {CXXFLAGS: "-fno-operator-names"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies_dpcpp.sh
     - name: Build & Install
@@ -241,7 +241,7 @@ jobs:
     #    #define select_impl_(_1, _2, impl_, ...) impl_
     env: {CXXFLAGS: "-Werror -Wall -Wextra -Wpedantic -Wnull-dereference -Wfloat-conversion -Wshadow -Woverloaded-virtual -Wextra-semi -Wunreachable-code -Wno-deprecated-declarations -Wno-gnu-zero-variadic-macro-arguments -Wno-pass-failed"}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies_hip.sh
     - name: Build & Install

.github/workflows/macos.yml

@@ -19,7 +19,7 @@ jobs:
     name: AppleClang@15.0 GFortran@15.1 [tutorials]
     runs-on: macos-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Dependencies
       run: .github/workflows/dependencies/dependencies_mac.sh
     - name: Build & Install

.github/workflows/style.yml

@@ -14,13 +14,13 @@ jobs:
   tabs:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
       - name: Tabs
         run: .github/workflows/style/check_tabs.sh
 
   trailing_whitespaces:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
       - name: Trailing Whitespaces
         run: .github/workflows/style/check_trailing_whitespaces.sh

.github/workflows/windows.yml

@@ -16,7 +16,7 @@ jobs:
     name: MSVC w/o Fortran w/o MPI
     runs-on: windows-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Build & Install
       run: |
         cd ExampleCodes