[docs] Add note in Contribute about the ipv6 restriction when using weboob gitlab with git+ssh

Status Job ID Name Coverage
  Build
passed #28788
build:3

00:00:59

 
  Test
passed #28791
load-modules:3

00:02:03

passed #28789
pyflakes:3

00:02:11

passed #28790
pyflakes-strict:3

00:02:21

passed #28792
unittests:3

00:01:51

failed #28793
allowed to fail
unittests-modules:3

00:10:23

 
  Deploy
passed #28794
doc:3

00:01:06

 
Name Stage Failure
failed
unittests-modules:3 Test
-----------------------------------------------------------------------
TOTAL 70566 41207 42%
----------------------------------------------------------------------
Ran 370 tests in 518.434s

FAILED (SKIP=112, errors=157, failures=31)
=== Total coverage ===
MODULES COVERAGE: 42%
ERROR: Job failed: exit code 1