Fix UrlPathHelper#shouldRemoveSemicolonContent() (#27303)

The checkReadOnly() method should only be called from
methods that modify properties to prevent modification
of read-only instances.

Fixes #27256

spring-web/src/test/java/org/springframework/web/util/UrlPathHelperTests.java

@@ -22,6 +22,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
 
 /**
  * Unit tests for {@link UrlPathHelper}.
@@ -165,6 +166,11 @@ public class UrlPathHelperTests {
 		assertThat(helper.getLookupPathForRequest(request)).isEqualTo("/welcome.html;c=d");
 	}
 
+	@Test // gh-27303
+	public void shouldRemoveSemicolonContentWithReadOnlyInstance() {
+		assertThatCode(UrlPathHelper.defaultInstance::shouldRemoveSemicolonContent).doesNotThrowAnyException();
+	}
+
 
 	//
 	// suite of tests root requests for default servlets (SRV 11.2) on Websphere vs Tomcat and other containers