Avoid Gradle build warnings about @⁠SuppressFBWarnings from FindBugs

In order to avoid Gradle build warnings about @⁠SuppressFBWarnings, this
commit introduces a testCompileOnly dependency on `findbugs` in the
spring-webmvc module so that the class file for @⁠SuppressFBWarnings is
available to the compileTestJava task.

Closes gh-34418

spring-webmvc/spring-webmvc.gradle

@@ -40,6 +40,9 @@ dependencies {
 	optional("org.reactivestreams:reactive-streams")
 	optional("org.webjars:webjars-locator-core")
 	optional("org.webjars:webjars-locator-lite")
+	testCompileOnly("com.google.code.findbugs:findbugs") {  // for groovy-templates
+		exclude group: "dom4j", module: "dom4j"
+	}
 	testImplementation(testFixtures(project(":spring-beans")))
 	testImplementation(testFixtures(project(":spring-context")))
 	testImplementation(testFixtures(project(":spring-core")))