ci: Reactor perf tests checkout step to checkout the code correctly. (#19267)

Earlier code wasn't checked out correctly when test-build-docker workflow ran, this PR adds conditional checkout.

.github/workflows/perf-test.yml

@@ -44,11 +44,19 @@ jobs:
         ports:
           - 27017:27017
     steps:
-      # Check out merge commit between the PR branch & base branch
-      - name: Fork based /perf-test checkout
+      - name: Checkout the merged commit from PR and base branch
+        if: inputs.pr != 0
         uses: actions/checkout@v3
         with:
-          ref: "refs/pull/${{ github.event.client_payload.pull_request.number }}/merge"
+          fetch-depth: 0
+          ref: refs/pull/${{ inputs.pr }}/merge
+
+      # Checkout the code in the current branch in case the workflow is called because of a branch push event
+      - name: Checkout the head commit of the branch
+        if: inputs.pr == 0
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
 
       - name: Figure out the PR number
         run: echo ${{ inputs.pr }}