firmata: try to stabilize tests

[gen2thomas]

Solved issues and/or description of the change

Firmata test "TestProcessDigitalRead4" (run "test_platforms") failed several times in succession on the server but works locally. Try to stabilize test by increasing the timeout from 20ms to 30ms.

Manual test

none

Checklist

• The PR's target branch is 'hybridgroup:dev'
• New and existing unit tests pass locally with my changes (e.g. by run make test_race)
• No linter errors exist locally (e.g. by run make fmt_check)
• I have performed a self-review of my own code