ci: apply standard Mergify rules for release branches too

It is not always possible to automatically backport PRs to release
branches. That also means that these backport PRs are not created by the
mergify[bot] account. Because of this, it is needed to manually merge
PRs, as Mergify refuses to do it.

By changing the `base=` option to match a regular expression that
includes both `devel` and `release-*` branches, Mergify should assist
with merging PRs to release branches too.

Note that the `ci/centos` branch is different, as runs other tests than
the normal branches.

Signed-off-by: Niels de Vos <ndevos@redhat.com>

.mergify.yml

@@ -15,7 +15,7 @@ defaults:
 pull_request_rules:
   - name: remove outdated approvals
     conditions:
-      - base=devel
+      - base~='^(devel)|(release-.+)$'
     actions:
       dismiss_reviews:
         approved: true
@@ -32,7 +32,7 @@ pull_request_rules:
   - name: automatic merge
     conditions:
       - label!=DNM
-      - base=devel
+      - base~='^(devel)|(release-.+)$'
       - "#approved-reviews-by>=2"
       - "#changes-requested-reviews-by=0"
       - "status-success=codespell"
@@ -58,7 +58,7 @@ pull_request_rules:
     conditions:
       - label!=DNM
       - label=ready-to-merge
-      - base=devel
+      - base~='^(devel)|(release-.+)$'
       - "#approved-reviews-by>=1"
       - "status-success=codespell"
       - "status-success=multi-arch-build"