Update bomr config to only suggest upgrades with same minor version

Now that we're in the RC phase and close to release, we only want to
pick up maintenance releases of our managed dependencies. This commit
updates bomr's config accordingly.

.bomr/bomr.yaml

@@ -6,7 +6,7 @@ bomr:
       repository: spring-boot
       issue-labels:
         - 'type: dependency-upgrade'
-    policy: same-major-version
+    policy: same-minor-version
     prohibited:
       - project: derby
         versions: