Fix tagging released Docker image on CI

Increase version to 4.6.0 (coturn#976)

Increase the version number for the 4.6.0 release.
It uses the codename Gorst.

Improve Docker CI pipeline

- omit publishing and releasing Docker images in forks
- verify Git tag to match Makefile before releasing
- auto-cancel concurrent CI pipelines for the same Git ref

Update Alpine to 3.16.2 version and Debian "bullseye" to 20220801 sna…

…pshot in Docker image to fix CVE-2022-37434

Update Alpine to 3.16.1 version and Debian "bullseye" to 20220622 sna…

…pshot in Docker image to fix CVE-2022-2097 and CVE-2022-30065

Upgrade Alpine to 3.15 version and Debian "bullseye" to 20220509 snap…

…shot in Docker image

Update Alpine to 3.15.4 version to fix CVE-2022-28391

Update Alpine to 3.15.3 version and Debian "bullseye" to 20220328 sna…

…pshot to fix CVE-2018-25032

Update Alpine to 3.15.2 version and Debian "bullseye" to 20220316 sna…

…pshot to fix CVE-2022-0778

Bump up Docker image version to 4.5.2-r8