tools: Make the "Allow commits" error more obnoxious.

Add ANSI codes and emoji so that the error stands out in the pipeline
output. Clarify the text.

tools/validate-commit.py

@@ -171,6 +171,12 @@ def verify_merge_request():
     gitlab_api_pfx = "https://gitlab.com/api/v4"
     # gitlab.com/wireshark/wireshark = 7898047
     project_id = os.getenv('CI_MERGE_REQUEST_PROJECT_ID')
+    ansi_csi = '\x1b['
+    ansi_codes = {
+        'black_white': ansi_csi + '30;47m',
+        'bold_red': ansi_csi + '31;1m', # gitlab-runner errors
+        'reset': ansi_csi + '0m'
+    }
     m_r_iid = os.getenv('CI_MERGE_REQUEST_IID')
     if project_id is None or m_r_iid is None:
         print("This doesn't appear to be a merge request. CI_MERGE_REQUEST_PROJECT_ID={}, CI_MERGE_REQUEST_IID={}".format(project_id, m_r_iid))
@@ -186,13 +192,10 @@ def verify_merge_request():
         try:
             if not m_r_attrs['allow_collaboration']:
                 print('''\
-ERROR: Please make sure the setting
-
-    Allow commits from members who can merge to the target branch
-
-is checked in your merge request so that maintainers can rebase your change
-and make minor edits.\
-''')
+{bold_red}ERROR:{reset} Please edit your merge request and make sure the setting
+    {black_white}✅ Allow commits from members who can merge to the target branch{reset}
+is checked so that maintainers can rebase your change and make minor edits.\
+'''.format(**ansi_codes))
                 return False
         except KeyError:
             sys.stderr.write('This appears to be a merge request, but we were not able to fetch the "Allow commits" status\n')