Polish bomr exclusion for the maven shade plugin

See gh-21265

Author: snicoll

.bomr/bomr.yaml

@@ -15,7 +15,7 @@ bomr:
       - project: maven-shade-plugin
         versions:
           # https://github.com/spring-projects/spring-boot/issues/21128
-          - '[3.2.3,)'
+          - '3.2.3'
   verify:
     ignored-dependencies:
       # Avoid conflicting transitive requirements for