Unskip and fix tests that fail depending on user's local .gemrc file.

[martinemde]

Description:

Without writing .gemrc, the gem source -a and -r don't work correctly. In particular, the presence of update_sources: true in .gemrc breaks one test, while writing the .gemrc fixes a previously skipped test.

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Tasks:

• Fixed local tests for different .gemrc configurations.
• Un-skipped a test that works now with .gemrc written.

I will abide by the code of conduct.

[martinemde]

Hey @segiddins, looks like you already took a stab at something like this in #401. This is passing and works for me locally on 3.1, 3.2, 3.3, and 3.4. The catch seems to be if you have update_sources: true in ~/.gemrc.