Runner tests: Read CODEQL_RUNNER from the stored JSON

This test workflow does not source the environment from the init step,
so we need to manually read in the variable.

Author: adityasharad

Diff for: .github/workflows/pr-checks.yml

@@ -414,6 +414,7 @@ jobs:
       - name: Build code
         shell: bash
         run: |
+          CODEQL_RUNNER="$(cat codeql-runner/codeql-env.json | jq -r '.CODEQL_RUNNER')"
           $CODEQL_RUNNER ../action/runner/dist/codeql-runner-macos autobuild
 
       - name: Run analyze