Check test RBI files for well-formedness

[paracycle]

Motivation

@ryanwilsonperkin caught a problem with the RBI output in Active Record relations generator, which reminded me that we should be checking RBI files for well-formedness automatically in every test.

Implementation

After every RBI file is generated as a string, we pass it through Sorbet and just check the error-code. If there is an error, we show the Sorbet output which should help figure out the problem.

Tests

No automated test cases.