[SPARK-30173] Tweak stale PR message

Follow-on to #26877.

### What changes were proposed in this pull request?

This PR tweaks the stale PR message to [clarify](https://github.com/apache/spark/pull/24457#issuecomment-571393900) the procedure for reopening a PR after it has been marked as stale.

### Why are the changes needed?

This change should clarify the reopening process for contributors.

### Does this PR introduce any user-facing change?

No.

### How was this patch tested?

N/A

Closes #27114 from nchammas/SPARK-30173-stale-tweaks.

Authored-by: Nicholas Chammas <nicholas.chammas@gmail.com>
Signed-off-by: Sean Owen <srowen@gmail.com>

.github/workflows/stale.yml

@@ -11,12 +11,13 @@ jobs:
     - uses: actions/stale@v1.1.0
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
-        stale-pr-message: |
+        stale-pr-message: >
           We're closing this PR because it hasn't been updated in a while.
           This isn't a judgement on the merit of the PR in any way. It's just
           a way of keeping the PR queue manageable.
 
-          If you'd like to revive this PR, please reopen it!
+          If you'd like to revive this PR, please reopen it and ask a
+          committer to remove the Stale tag!
         days-before-stale: 100
         # Setting this to 0 is the same as setting it to 1.
         # See: https://github.com/actions/stale/issues/28