tests: add SkipInstall option for pulumitest tests

[rquitales]

Proposed changes

This PR explicitly sets the opttest.SkipInstall() option for our yaml tests. It is observed that the test framework/automation API is unable successfully run pulumi install prior to the other pulumi operations. This error was hit in the presubmit for #3046, but went unnoticed in the past due to the TestTerraformConvert installing the right plugins before the other tests hit the installation step.

Manual validation:

• Deleted the local ~/.pulumi/plugin folder
• Run the tests without the changes and notice the test errors
• Run the tests with the changes here and they pass

Related issues (optional)

Fixes: #3048

[github-actions]

Does the PR have any schema changes?

Looking good! No breaking changes found.
No new resources/functions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.75%. Comparing base (1100978) to head (f6165e9).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3049      +/-   ##
==========================================
- Coverage   36.77%   36.75%   -0.03%     
==========================================
  Files          71       71              
  Lines        9262     9262              
==========================================
- Hits         3406     3404       -2     
- Misses       5518     5519       +1     
- Partials      338      339       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.