Branches with # in the name do not list the file tree with vue refactor

Summary

Posted on twitter, when the vue_file_list feature flag is enabled, repository files do not display for branches with # in the name.

This bug will block enabling the feature flag since there is no workaround to seeing your files in these branches.

Steps to reproduce

1. Create a master branch with a README.md
2. Create a branch from master with # in the URL such as branch-with-number-sign-#
3. View the file tree for branch-with-number-sign-#

Example Project

An example project can be found here (confirmed broken before the feature flag was disabled) https://gitlab.com/fremue85/gitlab-wont-show-tree-of-files-in-branches-with-number-sign-anymore/-/branches

What is the current bug behavior?

The file tree page loads, but the file tree is empty.

What is the expected correct behavior?

There should be files in the tree, at least a README.md

Output of checks

This bug happens on GitLab.com

/cc @iamphill