run tests + upload coverage report to codecov on push into main

[armcknight]

Related work in other demos: https://github.com/vlad-ko/laravel-stripe-app-gh/pull/50 and https://github.com/sentry-demos/empower/pull/414

[armcknight]

Notes from meeting today with @yuval-sentry:

• need to put something like https://github.com/getsentry/sentry-cocoa/blob/46267d8dc658d3dda8d825c2e8792717f828dcb0/.github/workflows/test.yml#L242-L266 after the coverage report here https://github.com/sentry-demos/ios/blob/e36f129970ae7ef907d21804ef109ad5914ab99d/.github/workflows/test.yml#L28
• the test workflow currently fails: https://github.com/sentry-demos/ios/actions/workflows/test.yml
• want a way to run a test/codecov job once per day and also with a manual trigger
• there's currently another workflow here: https://github.com/sentry-demos/ios/blob/master/.github/workflows/upload-codecov-report.yml that was an experiment

currently working on getting test.yml building and running tests, then will add the coverage step from upload-codecov-report.yml and delete upload-codecov-report.yml.

tracking work in https://github.com/sentry-demos/ios/pull/83