fix regex for longer slack webhook urls and added another error response

detect_secrets/plugins/slack.py

@@ -18,9 +18,7 @@ class SlackDetector(RegexBasedDetector):
         re.compile(r'xox(?:a|b|p|o|s|r)-(?:\d+-)+[a-z0-9]+', flags=re.IGNORECASE),
         # Slack Webhooks
         re.compile(
-            r"""
-            https://hooks.slack.com/services/T[a-zA-Z0-9_]{8}/B[a-zA-Z0-9_]{8}/[a-zA-Z0-9_]{24}
-            """,
+            r'https://hooks.slack.com/services/T[a-zA-Z0-9_]+/B[a-zA-Z0-9_]+/[a-zA-Z0-9_]+',
             flags=re.IGNORECASE | re.VERBOSE,
         ),
     )
@@ -33,7 +31,7 @@ def verify(self, token, **kwargs):  # pragma: no cover
                     'text': '',
                 },
             )
-            valid = response.text == 'missing_text_or_fallback_or_attachments'
+            valid = response.text in ['missing_text_or_fallback_or_attachments', 'no_text']
         else:
             response = requests.post(
                 'https://slack.com/api/auth.test',