Check out without actions/checkout in CI

actions/checkout is a JavaScript action and the swift image has no node, so
the first run failed at exec: "node": executable file not found before any
Swift step ran. Replaced with a plain git fetch of the SHA, falling back to
the ref for servers without allowAnySHA1InWant.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01C5X1tYo9oxAfvoiFMh1QQr

.gitea/workflows/test.yml

@@ -13,7 +13,23 @@ jobs:
       # not a surprise on an unrelated push.
       image: swift:6.2
     steps:
-      - uses: actions/checkout@v4
+      # Checked out by hand rather than with actions/checkout, which is a
+      # JavaScript action — it needs `node` in the container, and the Swift
+      # image has no reason to ship one.
+      - name: Checkout
+        env:
+          GITEA_TOKEN: ${{ github.token }}
+        run: |
+          set -eu
+          git init -q .
+          git config --local http.extraheader \
+            "Authorization: Basic $(printf 'x-access-token:%s' "$GITEA_TOKEN" | base64 -w0)"
+          git remote add origin "$GITHUB_SERVER_URL/$GITHUB_REPOSITORY.git"
+          # Fetching the exact SHA needs uploadpack.allowAnySHA1InWant on the
+          # server; fall back to the ref, which every server allows.
+          git fetch --depth 1 origin "$GITHUB_SHA" \
+            || git fetch --depth 1 origin "$GITHUB_REF"
+          git checkout -q FETCH_HEAD
 
       - name: Toolchain
         run: swift --version