Increasing timeouts for linter tests

[gracegoo-stripe]

r? @etsai-stripe

These tests have been intermittently failing due to timeouts: https://github.com/stripe/vscode-stripe/runs/4121204401?check_suite_focus=true

The open and show document functions can take a couple of seconds in the worst case scenario which will cause the test to timeout (the default is 2 seconds). Even for ones that do pass, we always come close to the timeout in the first two test cases.

See logs added here: https://github.com/stripe/vscode-stripe/runs/4159081815?check_suite_focus=true.

Doc open took: 245 ms
Doc show took: 126 ms
Test set up took 374 ms
Linter construction took 1 ms
File is ignored by git? true
Linter.activate took  2 ms
Test cleanup  1 ms
      ✔ Editor content is not searched when file is git-ignored (379ms)