From 11.5 and forward, we will use a new branching structure in git.
Which branch of core you want to use in 11.5 depends on your purpose.

Official Branch - version/version number/official

• Examples:
  • version/11.5/official
  • version/12.0/official
• Contains code to the officially released code (after release).
• Use this branch if you want to test against what the user is actually using.

Beta Branch - version/version number/beta

• Examples:
  • version/11.5/beta
  • version/12.0/beta
• Contains code to the Public RC/Beta box.
• Use this for migration or testing for the next release version.