Occassional PROTOCOL_ERRORs during Darwin builds

Recently we have been seeing occasional errors of the form:

git fetch -f https://gitlab.haskell.org/ghc/ghc-performance-notes.git refs/notes/perf:refs/notes/perf
error: RPC failed; curl 92 HTTP/2 stream 0 was not closed cleanly: PROTOCOL_ERROR (err 1)
fatal: the remote end hung up unexpectedly

from Darwin builds. One diagnosis of the issue can be found on StackOverflow. This isn't the first time this has come up: I thought I had resolved this with a workaround in the runner configuration (increasing the POST buffer size) in ci-config@ac7742ea. This seemed to work previously but the issue has again appeared on the new Darwin runners despite the workaround being applied.