Improve diagnostic for PrepareDepsOfTargetsUnderDirectoryFunctionTest

We've been hitting a (flaky?) bug in CI that we haven't been able to reproduce locally yet. The failure is here, so this assertion change should help us see what the actual error message is.

PiperOrigin-RevId: 355062974

src/test/java/com/google/devtools/build/lib/skyframe/PrepareDepsOfTargetsUnderDirectoryFunctionTest.java

@@ -15,6 +15,7 @@
 package com.google.devtools.build.lib.skyframe;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.devtools.build.skyframe.EvaluationResultSubjectFactory.assertThatEvaluationResult;
 import static com.google.devtools.build.skyframe.WalkableGraphUtils.exists;
 
 import com.google.common.base.Preconditions;
@@ -82,7 +83,7 @@ private EvaluationResult<?> getEvaluationResult(SkyKey... keys) throws Interrupt
             .build();
     EvaluationResult<PrepareDepsOfTargetsUnderDirectoryValue> evaluationResult =
         skyframeExecutor.getDriver().evaluate(ImmutableList.copyOf(keys), evaluationContext);
-    Preconditions.checkState(!evaluationResult.hasError());
+    assertThatEvaluationResult(evaluationResult).hasNoError();
     return evaluationResult;
   }