bug/Install-workflow-fails-with-404

[bwalsh]

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Title: Install workflow fails with 404 error when using tags

Description:
The Install Script Test workflow fails with a 404 error when triggered on tags/releases.

Failed Job:
https://github.com/calypr/git-drs/actions/runs/21888122076/job/63187816255

Error:

curl: (56) The requested URL returned error: 404
##[error]Process completed with exit code 1.

Root Cause:
The workflow hardcodes /refs/heads/ in the install script URL, but tags are not under this path.

Solution:
Remove /refs/heads/ from the URL and use the ref name directly so the script works for both branches and tags.