Update pbr requirement from >=1.9 to >=7.0.3

Updates the requirements on [pbr](https://docs.openstack.org/pbr/latest/) to permit the latest version.

---
updated-dependencies:
- dependency-name: pbr
  dependency-version: 7.0.3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -2,7 +2,7 @@ https://github.com/faucetsdn/python3-fakencclient/archive/main.tar.gz#egg=ncclie
 chewie==0.0.25
 eventlet>=0.34.3; python_version >= "3.12"
 networkx>=1.9
-pbr>=1.9
+pbr>=7.0.3
 prometheus_client==0.25.0
 ruamel.yaml==0.18.16
 os_ken==3.1.0