Migrate usages of Truth8.assertThat to equivalent usages of Truth.assertThat.

The `Truth8` methods will be hidden in the future. All callers will use `Truth`.

To make that migration possible, upgrade Truth to 1.3.0.

(progress toward google/truth#746)

PiperOrigin-RevId: 603108718

Author: cpovirk

core/src/test/java/com/google/errorprone/bugpatterns/collectionincompatibletype/TruthIncompatibleTypeTest.java

@@ -458,7 +458,7 @@ public void streamContainsExactly() {
     compilationHelper
         .addSourceLines(
             "Test.java",
-            "import static com.google.common.truth.Truth8.assertThat;",
+            "import static com.google.common.truth.Truth.assertThat;",
             "import com.google.common.collect.Multimap;",
             "import java.util.stream.Stream;",
             "public class Test {",