[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>
2 files changed