pgtest: test invalid param binding

[maddyblue]

This fixes the test_bind_params flake.

Testing this with tokio_postgres as the driver causes the driver to return the WrongType error message. Wireshark showed that the bind request was never issued to the server. The test flake must be happening because the driver's type cache either is or isn't yet populated, and so it does end up issuing the bind request to the server which returns the no overload error.

Motivation

• This PR fixes a previously unreported bug.

Checklist

• [ ] This PR has adequate test coverage / QA involvement has been duly considered.

• [ ] This PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way) and therefore is tagged with a T-protobuf label.

• [ ] This PR includes the following user-facing behavior changes:

  • n/a