Create SCL branches in gcc-toolset-12

The version of gcc-toolset-12 is behind RHEL, so it needs to be rebuilt. However, we're missing the appropriate branches in CentOS. Can you please create:

• scl-gcc-toolset-12-rhel-9.3.0
• scl-gcc-toolset-12-rhel-9.4.0
• scl-gcc-toolset-12-rhel-8.9.0
• scl-gcc-toolset-12-rhel-8.10.0

in 'gcc-toolset-12'?