custom_check: Improve check for exit(...) call in management commands.

It's better for this to catch all exit(...) calls with non-zero exit
code, given the purpose is to catch all exits with failure, as opposed
to only exit(1).

tools/linter_lib/custom_check.py

@@ -456,7 +456,7 @@ python_rules = RuleList(
             ],
         },
         {
-            "pattern": "exit[(]1[)]",
+            "pattern": r"exit[(][1-9]\d*[)]",
             "include_only": {"/management/commands/"},
             "description": "Raise CommandError to exit with failure in management commands",
             "exclude": {"zerver/management/commands/process_queue.py"},