SCM Provider Generator pathsExists false positives for gitlab < 17.7 users

[rbounds]

Checklist:

• I've searched in the docs and FAQ for my answer: https://bit.ly/argocd-faq.
• I've included steps to reproduce the bug.
• I've pasted the output of argocd version.

Describe the bug
In argocd v2.14 the gitlab service for the scm provider generator was updated to support gitlab >= 17.7 which now returns a 404 instead of a 200 for repositoires.ListTree(). While that is great for users of gitlab >= 17.7 it seems to break the SCM provider for users that have not upgraded their gitlab instance.

Users using gitlab < 17.7 will get a 200 with an empty array which will incorrectly return a positive for pathsExist filters

To Reproduce

Reproducing is difficult because it requires a running gitlab instance < 17.7. Assuming that can be overcome you'd simply create an applicationset that uses the scm provider generator and a pathsExists Filter:

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: myapps
spec:
  generators:
  - scmProvider:
      filters:
        - pathsExist: ["nonexistent-file.yaml"]
      gitlab:
        group: "8675309"
        api: https://gitlab.example.com/

Expected behavior
I'd prefer it the scm provider also handled older versions of gitlab by checking if the result from repository.ListTree() was an empty on a HTTP 200 response. This should let the pathsExists filter work regardless of gitlab version.

Version
I don't use the argocd cli, but argocd version from the applicaionset-controller container:
argocd: v2.14.8+a7178be
BuildDate: 2025-03-24T20:54:41Z
GitCommit: a7178be
GitTreeState: clean
GoVersion: go1.23.3
Compiler: gc
Platform: linux/arm64