Use supported checkout action in Gitea workflows

.gitea/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
     name: Rust, web and container
     runs-on: ubuntu-latest
     steps:
-      - uses: builtin:checkout
+      - uses: actions/checkout@v5
       - name: Verify Linux runner
         run: |
           set -eu
@@ -56,7 +56,7 @@ jobs:
     name: Windows launcher
     runs-on: windows-latest
     steps:
-      - uses: builtin:checkout
+      - uses: actions/checkout@v5
       - name: Verify Windows runner
         shell: pwsh
         run: |
@@ -84,7 +84,7 @@ jobs:
     runs-on: ubuntu-latest
     continue-on-error: true
     steps:
-      - uses: builtin:checkout
+      - uses: actions/checkout@v5
       - name: Verify runner
         run: |
           test "$(uname -s)" = Linux