Make TestContextManager.getTestContext() public

This commit changes the visibility of the getTestContext() method in
TestContextManager from 'protected' to 'public' in order to support
test method injection in JUnit 5 and similar use cases.

Issue: SPR-14011

spring-test/src/main/java/org/springframework/test/context/TestContextManager.java

@@ -124,7 +124,7 @@ public class TestContextManager {
 	/**
 	 * Get the {@link TestContext} managed by this {@code TestContextManager}.
 	 */
-	protected final TestContext getTestContext() {
+	public final TestContext getTestContext() {
 		return this.testContext;
 	}