Broken build due to failed `linkcheck` job

[atugushev]

I've noticed that matrix badges are frequently inaccessible, see README:

Sometimes, a certain issue even results in CI builds breaking (caught in #1973):

broken    https://img.shields.io/matrix/pip-tools:matrix.org?label=Discuss%20on%20Matrix%20at%20%23pip-tools%3Amatrix.org&logo=matrix&server_fqdn=matrix.org&style=flat - 408 Client Error: Request Timeout for url: https://img.shields.io/matrix/pip-tools:matrix.org?label=Discuss%20on%20Matrix%20at%20%23pip-tools%3Amatrix.org&logo=matrix&server_fqdn=matrix.org&style=flat

Perhaps we should consider ignoring https://img.shields.io/matrix as well?

/cc @webknjaz

[webknjaz]

Yes, that makes sense.