[CI] Conform to re2 regexes in branch config

Zuul has deprecated Perl-style syntax; and we're
getting warnings posted against the manifests:

 The RE2 syntax error is: invalid perl operator: (?!

Change-Id: I498573532fd701b47684a54bda9b54b86836afdc
Signed-off-by: Goutham Pacha Ravi <gouthampravi@gmail.com>
diff --git a/zuul.d/manila-tempest-stable-jobs.yaml b/zuul.d/manila-tempest-stable-jobs.yaml
index e59b5fb..0fb38ab 100644
--- a/zuul.d/manila-tempest-stable-jobs.yaml
+++ b/zuul.d/manila-tempest-stable-jobs.yaml
@@ -7,7 +7,7 @@
       Test the scenario test cases on the generic driver multibackend
       (DHSS=True) with NFS and CIFS
     parent: manila-tempest-plugin-generic-scenario-base
-    branches: &manila_tempest_image_pinned_branches ^(stable/(2023.1|zed|yoga|xena)).*$
+    branches: &manila_tempest_image_pinned_branches ^stable/(2023.1|zed|yoga|xena)$
     vars: &manila_tempest_image_pinned_vars
       devstack_localrc:
         # NOTE(carloss): Pinning manila service image to a Focal version,
@@ -65,7 +65,7 @@
 - job:
     name: manila-tempest-plugin-lvm-fips-stable
     parent: manila-tempest-plugin-lvm-fips-base
-    branches: ^(stable/(yoga|xena)).*$
+    branches: ^stable/(yoga|xena)$
     vars: *manila_tempest_image_pinned_vars
 
 - job: