[v0.13.0-beta1 regression] /run/buildkit is inaccessible for socket users

[AkihiroSuda]

The following /etc/buildkit/buildkitd.toml configuration is useless in BuildKit v0.13 (beta) because /run/buildkit is not accessible for GID=1001

[grpc]
  gid=1001

v0.12.5 (works):

$ ls -ldn /run/buildkit/
drwxrwx--- 2 0 1001 60 Feb  3 16:31 /run/buildkit/
$ ls -ln /run/buildkit/buildkitd.sock 
srw-rw---- 1 0 1001 0 Feb  3 16:31 /run/buildkit/buildkitd.sock

v0.13.0-beta1, beta2, beta3 (broken):

$ ls -ldn /run/buildkit/
drwxrwx--- 2 0 0 80 Feb  3 16:32 /run/buildkit/
$ ls -ln /run/buildkit/buildkitd.sock 
ls: cannot access '/run/buildkit/buildkitd.sock': Permission denied

[AkihiroSuda]

Regression in a7690c5 set tracing socket path to runtime dir (#4078)

[AkihiroSuda]

PR

• Fix regression /run/buildkit is inaccessible for socket user #4619