Update checkout to v7

Author: stertooy

README.md

@@ -98,7 +98,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - uses: gap-actions/setup-gap@v3
       - uses: gap-actions/build-pkg@v3
       - uses: gap-actions/run-pkg-tests@v4