Document how trigger rebaseline from the command line. NFC (#25662)

Once can use the `gh` (github command line tool) command rather than
having to use the website.

Author: sbc100

.github/workflows/ci.yml

@@ -71,10 +71,15 @@ jobs:
             echo ""
             echo "Test expectations are out-of-date on the target branch."
             echo "Please run the 'Rebaseline Tests' github action on the target"
-            echo "branch (normally 'main') before proceeding."
+            echo "branch (normally 'main') before proceeding.  You can do this"
+            echo "from the web UI or from the command line:"
             echo ""
-            echo "You can also run './tools/maint/rebaseline_tests.py --new-branch'"
-            echo "and use it to create a seperate PR."
+            echo "  gh workflow run rebaseline-tests.yml"
+            echo ""
+            echo "You can also run the following command locally and upload"
+            echo "your own PR:"
+            echo ""
+            echo "  ./tools/maint/rebaseline_tests.py --new-branch'"
             exit 1
           fi
       - name: Check test expectations on PR branch