Replace deprecated perl-style regex

Zuul deprecated usage of perl-style regex.

```
  All regular expressions must conform to RE2 syntax, but an
  expression using the deprecated Perl-style syntax has been detected.
  Adjust the configuration to conform to RE2 syntax.
```

Change-Id: I0dd4596cb0138e44122486e699b8f64714e8418a

.zuul.yaml

@@ -6,7 +6,9 @@
       Run unit tests with main branch of SQLAlchemy, alembic and oslo.db.
       Takes advantage of the base tox job's install-siblings feature.
     # The job only tests the latest and shouldn't be run on the stable branches
-    branches: ^(?!stable)
+    branches:
+      regex: ^stable/.*$
+      negate: true
     required-projects:
       - name: github.com/sqlalchemy/sqlalchemy
         override-checkout: main

test-requirements.txt

@@ -24,7 +24,7 @@ psycopg2>=2.8.0 # LGPL/ZPL
 
 # test
 pydotplus>=2.0.2 # MIT License
-hacking<2.1,>=2.0
+hacking<6.2.0,>=6.1.0
 oslotest>=3.2.0 # Apache-2.0
 testtools>=2.2.0 # MIT
 testscenarios>=0.4 # Apache-2.0/BSD