How to open MR from my fork against the upstream repo

**Describe the bug**
When I use the open to open a MR (gitlab in my case), the URL which lazygit open is against the origin repo, and not from my repo/fork against the origin repo.

**To Reproduce**
Steps to reproduce the behavior:

In my lazygit config, I have these lines,
```yaml
services:
'gitlab.example.com': gitlab:example.com
```
0. Have 2 remotes, `origin` and `my-fork`
1. From your local branch (which use my-fork us the upstream) press `o`
2. The URL for the MR which open in the URL is with
```
https://example.com///-/merge_requests/new?merge_request[source_branch]=
3. Need to manaully change the `` to `` to let the UI load the MR correctly, but even then is only aginst `master` and not the base of ``

```
**Expected behavior**
Press `o` and URL should be from my fork against the source of my branch.

**Screenshots**

**Version info:**
```
❯ git --version
git version 2.47.0

❯ lazygit --version
commit=611fabde11d24d9acc71ee26077b9a1101f59f27, build date=2024-09-18T10:56:10Z, build source=binaryRelease, version=0.44.1, os=linux, arch=amd64, git version=2.47.0
```
**Additional context**