Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...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>

Author: dependabot[bot]

.github/workflows/build.yaml

@@ -16,7 +16,7 @@ jobs:
         python-version: ["3.11", "3.12", "3.13", "3.14"]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           # Need to clone everything to determine version from git.
           fetch-depth: 0
@@ -74,7 +74,7 @@ jobs:
     if: startsWith(github.ref, 'refs/tags/')
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           # Need to clone everything to embed the version.
           fetch-depth: 0

.github/workflows/build_docs.yaml

@@ -10,7 +10,7 @@ jobs:
   build_sphinx_docs:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           # Need to clone everything for the git tags.
           fetch-depth: 0

.github/workflows/codeql-analysis.yml

@@ -42,7 +42,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       # Initializes the CodeQL tools for scanning.
       - name: Initialize CodeQL

.github/workflows/do_not_merge.yaml

@@ -26,7 +26,7 @@ jobs:
             'DO NOT MERGE'. Remove this commit from the branch before merging
             or change the commit summary."
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Check requirements.txt for branches
         shell: bash

.github/workflows/docstyle.yaml

@@ -14,7 +14,7 @@ jobs:
   numpydoc:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v6