Fixed report-merged-pr action (#41270)

### What does this PR do?

If the PR has multiple PR numbers, we should take the last one and not fail. (see this [failure](https://github.com/DataDog/datadog-agent/actions/runs/18007355149/job/51230702806))

### Motivation

### Describe how you validated your changes

### Additional Notes

Author: CelianR

.github/workflows/report-merged-pr.yml

@@ -33,7 +33,7 @@ jobs:
           echo "Last commit message: $COMMIT_MESSAGE"
 
           # Extract PR number from format "(#1234)" in commit message
-          PR_NUMBER=$(echo "$COMMIT_MESSAGE" | grep -oE '\(#[0-9]+\)' | grep -oE '[0-9]+')
+          PR_NUMBER="$(echo "$COMMIT_MESSAGE" | grep -oE '\(#[0-9]+\)' | grep -oE '[0-9]+' | tail -n 1)"
 
           # If no PR number found in commit message, exit with error
           if [ -z "$PR_NUMBER" ]; then