Fix negative lookahead assertion syntax error

Python regexes are deprecated in Zuul, so this commit updates the
configuration to use RE2-compatible syntax.

Change-Id: I19b81e4999f9c130e18872593df9dccb416e9e6a

zuul.d/ironic-python-agent-jobs.yaml

@@ -104,8 +104,10 @@
       - ^ironic_python_agent/tests/.*$
       - ^releasenotes/.*$
       - ^setup.cfg$
-      - ^tools/(?!bandit.yml).*$
       - ^tox.ini$
+      - ^tools/.*$
+      - regex: ^tools/bandit\.yml$
+        negate: true
 
 - job:
     name: ipa-tox-examples
@@ -120,8 +122,9 @@
       - ^ironic_python_agent/tests/.*$
       - ^releasenotes/.*$
       - ^setup.cfg$
-      - ^tools/(?!bandit.yml).*$
       - ^tox.ini$
+      - regex: ^tools/bandit\.yml$
+        negate: true
 
 # used by ironic-python-agent-builder
 - job: