test: refactor RunPagesProcess function to take functional arguments

What does this MR do?

Refactor the RunPagesProcess function in the tests to take functional arguments.

This was actually done in a previous MR but there were a few leftover tests using old functions (runPagesWithAuth and runPagesWithAuthAndEnv). I've also removed two unused functions: RunPagesProcessWithoutGitLabStub and RunPagesProcessWithEnvs

Closes #79 (closed)

TODO

• I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines