There was a PR which was merged into master, and the build fails with "couldn't find remote ref refs/pull/2/merge".

Just in case, the info below has any relevance to the problem:
develop has not been updated back from master;
the PR was originally branched out develop;
the PR was forked rather then checked out.

Any help would be appreciated.

gradle.yml :

name: Java CI

on: 
  push:
    branches:
      - develop
  pull_request: 
    branches: 
      - master
      - develop         
......

Log:

Run actions/checkout@v1
Syncing repository: XYZ
git version
git version 2.43.2
git lfs version
git-lfs/3.5.1 (GitHub; linux amd64; go 1.21.8)
git init "/home/runner/work/XYZ/XYZ"
hint: Using 'master' as the name for the initial branch. This default branch name
hint: is subject to change. To configure the initial branch name to use in all
hint: of your new repositories, which will suppress this warning, call:
hint: 
hint:   git config --global init.defaultBranch <name>
hint: 
hint: Names commonly chosen instead of 'master' are 'main', 'trunk' and
hint: 'development'. The just-created branch can be renamed via this command:
hint: 
hint:   git branch -m <name>
Initialized empty Git repository in /home/runner/work/XYZ/XYZ/.git/
git remote add origin https://github.com/XYZ
git config gc.auto 0
git config --get-all http.https://github.com/XYZ.extraheader
git -c http.extraheader="AUTHORIZATION: basic ***" fetch --tags --prune --progress --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/pull/2/merge:refs/remotes/pull/2/merge
Error: fatal: couldn't find remote ref refs/pull/2/merge
Warning: Git fetch failed with exit code 128, back off 1.611 seconds before retry.
git -c http.extraheader="AUTHORIZATION: basic ***" fetch --tags --prune --progress --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/pull/2/merge:refs/remotes/pull/2/merge
Error: fatal: couldn't find remote ref refs/pull/2/merge
Warning: Git fetch failed with exit code 128, back off 6.949 seconds before retry.
git -c http.extraheader="AUTHORIZATION: basic ***" fetch --tags --prune --progress --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/pull/2/merge:refs/remotes/pull/2/merge
Error: fatal: couldn't find remote ref refs/pull/2/merge
Error: Git fetch failed with exit code: 128
Error: Exit code 1 returned from process: file name '/home/runner/runners/2.316.0/bin/Runner.PluginHost', arguments 'action "GitHub.Runner.Plugins.Repository.v1_0.CheckoutTask, Runner.Plugins"