Release PBR 6.0.0

This adds PEP 660 editable mode support, to address problems with
pyproject.toml build isolation when installing packages with a
non-default Python interpreter, whose urgency is increased by the
need to start doing PEP 517 in projects that rely on WSGI
entrypoints now that pip 23.1 has started using its own fallback
pyproject.toml files.

This also removes support for Sphinx integration (broken with modern
versions of Sphinx and SetupTools), thus the major version increase.

Change-Id: I43939be790d1c817deeb769d9116be5a769df3f1

deliverables/_independent/pbr.yaml

@@ -237,5 +237,9 @@ releases:
     projects:
       - repo: openstack/pbr
         hash: 98c84b5f87b89573ea6930bc783f07f2dd5ae8fd
+  - version: 6.0.0
+    projects:
+      - repo: openstack/pbr
+        hash: 11151154b94f5e116c0ec8cd312df8d341553d50
 repository-settings:
   openstack/pbr: {}