CI: Race conditions

[chrysn]

With woodpecker, things are much better than with GitLab CI, but we still have

• Woodpecker runs all its steps on the same machine, concurrently if depends_on is set – and sometime the doc target writes to build while something else does too. Can we move doc's installation out of build? (Might involve copying around the aiocoap repo, given that it is installed using setuptools, or might involve a separate build step before doc so that it can be installed from a wheel)
• filelock is set to "fail if it's not available, don't time out", but the way that's expressed is with a 0.001 second timeout, and apparently at least once, the file system was too slow for that.