fixup semver check in CI

.github/workflows/ci.yml

@@ -127,13 +127,19 @@ jobs:
       run: cargo clippy --all --all-features -- -D warnings
 
   # Semver compatibility checks
-  # Note: This will fail until crates are published to crates.io
+  # Use git baseline since crates aren't published to crates.io yet
+  # See: https://github.com/obi1kenobi/cargo-semver-checks?tab=readme-ov-file#does-the-crate-im-checking-have-to-be-published-on-cratesio
   semver-checks:
     runs-on: ubuntu-latest
-    continue-on-error: true
+    # Only run on PRs (compare PR head against base branch)
+    if: github.event_name == 'pull_request'
 
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - name: Check semver
         uses: obi1kenobi/cargo-semver-checks-action@v2
+        with:
+          baseline-rev: ${{ github.event.pull_request.base.sha }}