ci(parse-server-mongo): detect step also requires helper script on base ref

parse-server-mongo/ already exists on main (PRs #94/#95), so the
prior detect step returned true on every PR's release-coverage
job and the measure step then tried to invoke a helper script
that didn't exist on the base ref. Extending detect to require
the helper script too lets the first-PR escape hatch fire when
the workflow itself is the change being introduced.

Signed-off-by: Akash Kumar <meakash7902@gmail.com>

Author: AkashKumar7902

.github/workflows/parse-server-mongo.yml

@@ -120,7 +120,7 @@ jobs:
       - id: detect
         name: Detect baseline presence
         run: |
-          if [ -d parse-server-mongo ] && [ -x parse-server-mongo/flow.sh ]; then
+          if [ -d parse-server-mongo ] && [ -x parse-server-mongo/flow.sh ] && [ -f .github/workflows/scripts/run-and-measure-parse-server.sh ]; then
             echo "sample-existed=true" >>"$GITHUB_OUTPUT"
             echo "Sample exists on base ref — running full measurement."
           else