Force to fetch upstream tags to not complain about existing tags with same name in origin (#896)

Author: creydr

openshift/release/mirror-upstream-branches.sh

@@ -23,7 +23,7 @@ set -exo pipefail
 TMPDIR=$(mktemp -d knativeFuncBranchingCheckXXXX -p /tmp/)
 readonly TMPDIR
 
-git fetch upstream --tags
+git fetch upstream --tags --force # use force to not complain about existing tags with same name in origin
 git fetch openshift
 
 # Ignore release 1.7-1.14 and only sync starting from 1.15