Use Java 11 Toolchain for OpenSaml4 compile

Issue gh-10816

saml2/saml2-service-provider/spring-security-saml2-service-provider.gradle

@@ -36,10 +36,19 @@ configurations {
 }
 
 compileOpensaml4MainJava {
+	javaCompiler = javaToolchains.compilerFor {
+		languageVersion = JavaLanguageVersion.of(11)
+	}
 	sourceCompatibility = '11'
 	targetCompatibility = '11'
 }
 
+compileOpensaml4TestJava {
+	javaCompiler = javaToolchains.compilerFor {
+		languageVersion = JavaLanguageVersion.of(11)
+	}
+}
+
 dependencies {
 	management platform(project(":spring-security-dependencies"))
 	api project(':spring-security-web')