Return Builder from sslInfo() builder method for MockServerHttpRequest

Prior to this commit, the sslInfo() method in MockServerHttpRequest's
BaseBuilder returned void, which prevented it from being used with the
intended fluent Builder pattern.

This commit changes the return type to the builder (B) for proper method
chaining.

Closes gh-35075

spring-test/src/test/java/org/springframework/mock/http/server/reactive/MockServerHttpRequestTests.java

@@ -25,6 +25,7 @@ import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
+import org.mockito.internal.util.MockUtil;
 
 import org.springframework.http.HttpCookie;
 import org.springframework.http.HttpHeaders;
@@ -33,6 +34,7 @@ import org.springframework.web.util.UriComponentsBuilder;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 import static org.junit.jupiter.api.Named.named;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link MockServerHttpRequest}.
@@ -66,6 +68,19 @@ class MockServerHttpRequestTests {
 		assertThat(request.getURI().toString()).isEqualTo("/foo%20bar?a=b&name%20A=value%20A1&name%20A=value%20A2&name%20B=value%20B1");
 	}
 
+	/**
+	 * Ensure that {@code sslInfo()} can be used with the fluent builder pattern.
+	 */
+	@Test  // gh-35075
+	void sslInfo() {
+		MockServerHttpRequest request = MockServerHttpRequest.get("/test")
+				.sslInfo(mock())
+				.build();
+
+		assertThat(request.getSslInfo()).as("is mock").satisfies(sslInfo -> MockUtil.isMock(sslInfo));
+		assertThat(request.getURI().toString()).isEqualTo("/test");
+	}
+
 	@ParameterizedTest(name = "[{index}] {0}")
 	@MethodSource
 	void httpMethodNotNullOrEmpty(ThrowingCallable callable) {