fix: release workflow checks out main HEAD and skips no-op versions

Two fixes: (1) checkout main instead of workflow_run.head_sha which can
be stale when commits land between CI start and release trigger, (2) skip
release if computed version matches what's already in source files.

Author: rileyhilliard

.github/workflows/release.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
-          ref: ${{ github.event.workflow_run.head_sha }}
+          ref: main
           fetch-depth: 0
           token: ${{ secrets.GITHUB_TOKEN }}
 
@@ -45,6 +45,14 @@ jobs:
             ver="${major}.${minor}.$((patch + 1))"
           fi
 
+          # Skip if computed version matches what's already in source
+          current=$(grep -Po '(?<=^__version__ = ")[^"]+' src/opendata_sdk/_version.py)
+          if [ "$ver" = "$current" ]; then
+            echo "skip=true" >> "$GITHUB_OUTPUT"
+            echo "Computed version ${ver} matches current, skipping"
+            exit 0
+          fi
+
           echo "version=${ver}" >> "$GITHUB_OUTPUT"
           echo "skip=false" >> "$GITHUB_OUTPUT"
           echo "Next version: ${ver}"