Change directory to inside checked out repo (ros-navigation#3493)

or relative path under $GITHUB_WORKSPACE
that actions/checkout places the repository

Author: ruffsl

.github/workflows/update_ci_image.yaml

@@ -27,6 +27,7 @@ jobs:
         id: check
         if: github.event_name == 'push'
         run: |
+          cd navigation2
           version=$(grep -oP '(?<=<version>).*?(?=</version>)' navigation2/package.xml)
           echo "version=${version}" >> $GITHUB_OUTPUT
           echo "trigger=true" >> $GITHUB_OUTPUT