Fix result collection if spawn is immediately done

Another small fix that I discovered running our existing tests.

Progress on #6394.

PiperOrigin-RevId: 239390890

src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java

@@ -788,6 +788,8 @@ public TestAttemptContinuation execute()
           return new BazelXmlCreationContinuation(
               resolvedPaths, xmlSpawnOutErr, builder, spawnResults, xmlContinuation);
         }
+        spawnResults = new ArrayList<>(spawnResults);
+        spawnResults.addAll(xmlContinuation.get());
       }
 
       TestCase details = parseTestResult(xmlOutputPath);