CI - Make Internal Tests less brittle (#3536)

# Description of Changes

For some reason, the Internal Tests have trouble fetching the commit
sha, especially when the job is re-run. This PR switches it to using ref
names rather than commit sha, because the ref names are much more
durable than GitHub's ephemeral commits that it generates during
workflows.

# API and ABI breaking changes

None. CI only.

# Expected complexity level and risk

1

# Testing

- [x] CI still passes
- [x] Ref still gets checked out successfully on re-run.

---------

Co-authored-by: Zeke Foppa <[email protected]>

Author: bfops

.github/workflows/internal-tests.yml

@@ -19,11 +19,6 @@ jobs:
     if: ${{ github.event_name != 'pull_request' || !github.event.pull_request.head.repo.fork }}
     runs-on: ubuntu-latest
     steps:
-      - name: Print current ref and sha
-        run: |
-          echo "github.ref=${{ github.ref }}"
-          echo "github.sha=${{ github.sha }}"
-
       - name: Trigger and wait for Internal Tests
         uses: actions/github-script@v7
         with:
@@ -33,9 +28,15 @@ jobs:
             const targetRepo = 'SpacetimeDBPrivate';
             const workflowId = 'internal-tests.yml';
             const targetRef = 'master';
-            const publicRef = context.sha;
+            // Use the ref for pull requests because the head sha is brittle (github does some extra dance where it merges in master).
+            const publicRef = (context.eventName === 'pull_request') ? context.payload.pull_request.head.ref : context.sha;
             const preDispatch = new Date().toISOString();
 
+            console.log("context.eventName =", context.eventName);
+            console.log("context.ref =", context.ref);
+            console.log("context.sha =", context.sha);
+            console.log("Dispatch workflow with publicRef =", publicRef);
+
             // Dispatch the workflow in the target repository
             await github.rest.actions.createWorkflowDispatch({
               owner: targetOwner,