Started getting URL using bad/illegal format or missing URL

[KristianBalaj]

Problem description

I have the following in my workflow to checkout a private repository (using MyOrg/some-repo just as an example):

      - name: Checkout some repository
        uses: actions/checkout@v4
        with:
          repository: MyOrg/some-repo
          path: ${{ env.TESTSUITE_DIR }}
          ref: main
          ssh-key: ${{ secrets.DEPLOY_KEY_SECRET }}

It was working before and suddenly I've started getting the following error:

Fetching the repository
  /usr/bin/git -c protocol.version=2 fetch --no-tags --prune --no-recurse-submodules --depth=1 origin +refs/heads/main*:refs/remotes/origin/main* +refs/tags/main*:refs/tags/main*
  Error: fatal: unable to access 'https://github.com:MyOrg/some-repo.git/': URL using bad/illegal format or missing URL
  The process '/usr/bin/git' failed with exit code 128
  Waiting 20 seconds before trying again

  /usr/bin/git -c protocol.version=2 fetch --no-tags --prune --no-recurse-submodules --depth=1 origin +refs/heads/main*:refs/remotes/origin/main* +refs/tags/main*:refs/tags/main*
  Error: fatal: unable to access 'https://github.com:MyOrg/some-repo.git/': URL using bad/illegal format or missing URL
  The process '/usr/bin/git' failed with exit code 128
  Waiting 18 seconds before trying again

  /usr/bin/git -c protocol.version=2 fetch --no-tags --prune --no-recurse-submodules --depth=1 origin +refs/heads/main*:refs/remotes/origin/main* +refs/tags/main*:refs/tags/main*
  Error: fatal: unable to access 'https://github.com:MyOrg/some-repo.git/': URL using bad/illegal format or missing URL
  Error: The process '/usr/bin/git' failed with exit code 128

This code was working in an action on 13 May and wasn't working on 12 June.

What I've tried

I've also tried to specify checkout version released before 13 May (i.e. v4.1.5) using the following:

      - name: Checkout some repository
        uses: actions/checkout@v4.1.5
        with:
          repository: MyOrg/some-repo
          path: ${{ env.TESTSUITE_DIR }}
          ref: main
          ssh-key: ${{ secrets.DEPLOY_KEY_SECRET }}

However, it failed with the same problem.

Also, I've tried to change the SSH key without any change.

[KristianBalaj]

Running rm ~/.gitconfig on the self-hosted machine resolved the issue.