fix: add missing call to EqualsTester#testEquals (#2307)

There needs to be a terminal call to `testEquals()` for the equals tester to do anything, this assertion is not currently being run.

This issue was found by https://errorprone.info/bugpattern/MissingTestCall

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/java-bigtable/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Rollback plan is reviewed and LGTMed
- [ ] All new data plane features have a completed end to end testing plan

Fixes #2292 ☕️

If you write sample code, please follow the [samples format](
https://github.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: cushon

google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/common/TypeTest.java

@@ -126,7 +126,8 @@ public void structWithSchema_equals() {
             StructWithSchema.fromProto(structProto.getStructType()))
         .addEqualityGroup(
             StructWithSchema.fromProto(complexStructProto.getStructType()),
-            StructWithSchema.fromProto(complexStructProto.getStructType()));
+            StructWithSchema.fromProto(complexStructProto.getStructType()))
+        .testEquals();
   }
 
   @Test