Fix: Enforce compiler warnings in oauth2-core

To prevent future compiler warnings from being introduced, this change
applies the `compile-warnings-error` plugin to the
`spring-security-oauth2-core` module.

This ensures that any new warnings will fail the build, maintaining
code quality and preventing warning accumulation.

Fixes: gh-18434
Signed-off-by: Pavel Vassiliev <paulvas@gmail.com>
Signed-off-by: paulvas <paulvas@gmail.com>

oauth2/oauth2-core/spring-security-oauth2-core.gradle

@@ -1,3 +1,7 @@
+plugins {
+	id 'compile-warnings-error'
+}
+
 apply plugin: 'io.spring.convention.spring-module'
 
 dependencies {