[bugfix] Try to fix the webfinger test, again

[daenney]

Description

For some reason we hit the case in CI where the TestFingerWithHostMetaCacheStrategy seems to experience some time dilation. It's possible this is a genuine bug, but I can't for the life of me reproduce it locally, even after having run this test thousands of times (-count=1000 when invoking go test etc.)

This changes the test to explicitly stop the webfinger cache, set TTL and Sweep frequency to something well beyond the lifetime of the cache during the test and then starts the cache again. Hopefully that does it, because the other option that remains is that for some reason timekeeping in CI/Docker is not as precise as when running the test on a host.

Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: [ ] -> [x]

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.

[tsmethurst]

fingers crossed!