When falling back to plain AssertionError, still include the "expected" and "but was" lines.

I have no idea what I was thinking when I went out of my way to omit them in CL 353141904.

And I think it had crossed my mind at one point to test the contents of the AssertionError, but I did not....

This CL does *not* address the main discussion of the day from #333 (comment); it's just *another* bug I noticed along the way. Sigh.

RELNOTES=When JUnit 4 is excluded from the classpath, the `AssertionError` Truth generates as a substitute for `ComparisonFailure` now includes the expected and actual values that were missing in 1.1.1.
PiperOrigin-RevId: 353319232

Author: cpovirk

core/src/main/java/com/google/common/truth/FailureMetadata.java

@@ -193,7 +193,7 @@ void failEqualityCheck(
       if (!isLinkageError(probablyJunitNotOnClasspath)) {
         throw probablyJunitNotOnClasspath;
       }
-      failure = new AssertionErrorWithFacts(messages, concat(headFacts, tailFacts), cause);
+      failure = new AssertionErrorWithFacts(messages, facts, cause);
     }
     doFail(failure);
   }

core/src/test/java/com/google/common/truth/NoJUnitTest.java

@@ -18,13 +18,20 @@
 
 import static com.google.common.truth.Truth.assertThat;
 
+import com.google.common.collect.ImmutableList;
+
 /** Truth-using binary to be run without JUnit on the classpath to verify that it still works. */
 public final class NoJUnitTest {
   public static void main(String[] args) {
     try {
       assertThat("a").isEqualTo("b");
       throw new Error("assertion should have failed");
     } catch (AssertionError expected) {
+      ImmutableList<Fact> facts = ((AssertionErrorWithFacts) expected).facts();
+      assertThat(facts.get(0).key).isEqualTo("expected");
+      assertThat(facts.get(0).value).isEqualTo("b");
+      assertThat(facts.get(1).key).isEqualTo("but was");
+      assertThat(facts.get(1).value).isEqualTo("a");
     }
   }