Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

This commit updates the connector tests to run locally. The previous use
of 127.0.0.2 does not work on non-Linux machines.

Also, this commit removes superfluous and duplicate tests that verify
exception paths, speeding up the test suite at the same time.

When the connector is closed, it must also close the underlying AlloyDB
gRPC-based client to avoid any errors. This ensures a clean shutdown of
the Connector generally.

This ensures the test doesn't leave any threads running, which otherwise
causes the test suite to hang until the test runner times out.

This will ensure breaking dependency changes are caught sooner, at the
cost of slower builds.

Updating automatic assignment to match primary/secondary maintainer roles.

This matches the official policy:
https://cloud.google.com/java/docs/supported-java-versions

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>