Some Environment Variables not Propagated by `test --runas`

[theory]

I found that running tests with --runas postgres would fail when I had a test that depended on the CARGO_MANIFEST_DIR environment variable. I fixed it in tembo-io/pg-jsonschema-boon@d7cb0d6 thanks to a suggestion by @eeeebbbbrrrr, but it seems like perhaps pgrx should manually propagate some relevant CARGO_* and RUST_* environment variables.