CI: updated checkout to v3

Author: malloch

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ jobs:
   Linux:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -28,7 +28,7 @@ jobs:
       CC: clang
       CXX: clang++
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -47,7 +47,7 @@ jobs:
   Windows-Latest:
     runs-on: windows-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         fetch-depth: 0
     - name: install dependencies