GeezerVison

Four links in the docs point at test files that moved in 1dcc378 (2021-12-14, "test: split up unit and integ tests"). Nothing else is touched.

Three of those are plain renames. The CONTRIBUTING.md one is not, so here is the reasoning in full.

1dcc378 moved the original file to test/integ/test_sendgrid.py (R100, content unchanged), and it is the only test_sendgrid.py that commit touched. A second one appeared later at test/unit/test_sendgrid.py, added by b5afcca (2023-11-24) with the GDPR region work, and it holds unit tests of the client host. The CONTRIBUTING sentence asks the reader to add unit tests, so it points there rather than at the file git paired the rename with. Say the word if you would rather it named both.

CONTRIBUTING.md is the file a first-time contributor is told to read, and its link to the test they are asked to edit has been a 404 for a little under five years.