Recognize -Djava.security.manager=allow

In the latest JDK versions, the string `allow` is not the name of a security
manager, and instead indicates that the code is allowed to install a security
manager of its own.

PiperOrigin-RevId: 455150087
Change-Id: Iac26ec13ffd006fc3a758678e36c94dcc94beec4

src/java_tools/junitrunner/java/com/google/testing/junit/runner/junit4/JUnit4Config.java

@@ -86,7 +86,7 @@ private JUnit4Config(
 
   private static boolean installSecurityManager(Properties systemProperties) {
     String securityManager = systemProperties.getProperty("java.security.manager");
-    if (securityManager != null) {
+    if (securityManager != null && !securityManager.equals("allow")) {
       return false; // Don't install over the specified security manager
     }
     return Boolean.valueOf(