ci: Change scheduled jobs to use the latest OVS stable branch.

Until now weekly OVN jobs would try to compile against OVS master
branch.  But that potentially contains changes that break API.  For
example a recent OVS commit [0] changed the signature of the
daemonize_start() function.  In order to avoid build failures due
to such changes, adapt the weekly OVN CI job to compile against the most
recent OVS stable branch commit.  Most likely that won't contain changes
that break APIs used by OVN.

[0] openvswitch/ovs@07cf581

Signed-off-by: Dumitru Ceara <dceara@redhat.com>
Acked-by: Ales Musil <amusil@redhat.com>

.github/workflows/test.yml

@@ -70,15 +70,23 @@ jobs:
       if: github.event_name == 'schedule'
       uses: actions/checkout@v3
 
-    # Weekly runs test using OVS master instead of the
-    # submodule.
-    - name: checkout OVS master
+    # Weekly runs test using the tip of the most recent stable OVS branch
+    # instead of the submodule.
+    - name: checkout OVS
       if: github.event_name == 'schedule'
       uses: actions/checkout@v3
       with:
         repository: 'openvswitch/ovs'
+        fetch-depth: 0
         path: 'ovs'
-        ref: 'master'
+
+    - name: checkout OVS most recent stable branch.
+      if: github.event_name == 'schedule'
+      run: |
+        git checkout \
+          $(git branch -a -l '*branch-*' | sed 's/remotes\/origin\///' | \
+            sort -V | tail -1)
+      working-directory: ovs
 
     - name: update APT cache
       run:  sudo apt update
@@ -156,15 +164,22 @@ jobs:
     - name: checkout without submodule
       if: github.event_name == 'schedule'
       uses: actions/checkout@v3
-    # Weekly runs test using OVS master instead of the
-    # submodule.
-    - name: checkout OVS master
+    # Weekly runs test using the tip of the most recent stable OVS branch
+    # instead of the submodule.
+    - name: checkout OVS
       if: github.event_name == 'schedule'
       uses: actions/checkout@v3
       with:
         repository: 'openvswitch/ovs'
+        fetch-depth: 0
         path: 'ovs'
-        ref: 'master'
+    - name: checkout OVS most recent stable branch.
+      if: github.event_name == 'schedule'
+      run: |
+        git checkout \
+          $(git branch -a -l '*branch-*' | sed 's/remotes\/origin\///' | \
+            sort -V | tail -1)
+      working-directory: ovs
     - name: install dependencies
       run:  brew install automake libtool
     - name: update PATH