[extractor/generic] Restrict --default-search schemeless URLs detection pattern (closes #21842)

youtube_dl/extractor/generic.py

@@ -2226,7 +2226,7 @@ class GenericIE(InfoExtractor):
                 default_search = 'fixup_error'
 
             if default_search in ('auto', 'auto_warning', 'fixup_error'):
-                if '/' in url:
+                if re.match(r'^[^\s/]+\.[^\s/]+/', url):
                     self._downloader.report_warning('The url doesn\'t specify the protocol, trying with http')
                     return self.url_result('http://' + url)
                 elif default_search != 'fixup_error':