Get the PR ref during checkout instead of using 'main'

Signed-off-by: Kyle Squizzato <[email protected]>

.github/workflows/build_test.yml

@@ -31,9 +31,20 @@ jobs:
       version: ${{ steps.vars.outputs.version }}
       clustername: ${{ steps.vars.outputs.clustername }}
     steps:
+      - name: Get PR ref
+        uses: actions/github-script@v6
+        id: pr
+        with:
+          script: |
+            const { data: pullRequest } = await github.rest.pulls.get({
+              ...context.repo,
+              pull_number: context.payload.pull_request.number,
+            });
+            return pullRequest
       - name: Checkout repository
         uses: actions/checkout@v4
         with:
+          ref: ${{fromJSON(steps.pr.outputs.result).merge_commit_sha}}
           fetch-depth: 0
       - name: Setup Go
         uses: actions/setup-go@v5