github: update mergify rules to use fedora 39, not 37

Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

.github/mergify.yml

@@ -15,7 +15,7 @@ queue_rules:
   - name: default
     conditions:
       - check-success=check-commits
-      - check-success=test (fedora-37)
+      - check-success=test (fedora-39)
       - check-success=test (fedora-38)
       - check-success=test (centos-stream9)
       - check-success=dpulls
@@ -34,7 +34,7 @@ pull_request_rules:
   - name: Automatic merge on approval
     conditions:
       - check-success=check-commits
-      - check-success=test (fedora-37)
+      - check-success=test (fedora-39)
       - check-success=test (fedora-38)
       - check-success=test (centos-stream9)
       - check-success=dpulls