[Tests] `nvm exec`/`nvm run`: add `--silent` tests

[jumbosushi]

As requested by @ljharb on issue #846, this pr adds tests for --silent flag for "run" and "exec" commands

The tests for "exec" seems to exist already but in a different naming convention, so I renamed to match other tests

[ljharb]

Thanks!!

[jumbosushi]

Hmm do you know why it's still failing? The output and expected output should be matching now 🤔 OUTPUT=<0.10.7> EXPECTED_OUTPUT=<v0.10.7> [ <0.10.7> = <v0.10.7> ]

[ljharb]

@jumbosushi are you still interested in completing this PR?

[ljharb]

@jumbosushi i've rebased this, but the tests are failing.