watch: Switch to github releases, the pypi release is missing the tests/testdata directory.

Add python3-pytest{,-runner} build dependencies.
7 jobs for master in 7 minutes and 9 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #352707
build

00:03:25

 
  Test
passed #352711
autopkgtest

00:03:11

passed #352712
blhc

00:01:14

passed #352710
lintian

00:01:27

passed #352713
piuparts

00:03:16

passed #352709
test-build-all

00:03:15

passed #352708
test-build-any

00:02:00