I would like to rename the 'master' branch to 'main' in the got.git
and diff.git repositories on git.gameoftrees.org in order to match the
default used by 'got init'. Note that got-www.git already uses 'main'.

It seems that simply running 'git branch -m' would be enough to switch
the server's repository over. Once the branch has been renamed with
that method, Git users will see this:

 $ git pull
 [...]
  * [new branch]        main       -> origin/main
  Your configuration specifies to merge with the ref 'refs/heads/master'
  from the remote, but no such ref was fetched.

And got users will see:

 $ got fetch
 [...]
 Fetched 24959d7c9d8bfb97fa2b67b3eb642bb040515b1d.pack
 Created reference refs/remotes/origin/main: c8c7d149feda16fa5f471654738791b6e7f1
af5e
 Created reference refs/heads/main: c8c7d149feda16fa5f471654738791b6e7f1af5e
 Created reference refs/remotes/origin/HEAD: refs/remotes/origin/main

I think in either case it is clear what happened, and what action
needs to be taken to continue working against the main branch (simply
run the same commands as usual, using 'main' instead of 'master').