chore(CI): Revert nightly AppImage name to "nightly"

Changed in 41a555def9, I think by accident.
Causes our release uploader to no longer replace the old version, instead
adding a new version each time it runs.

Keeping named overwrite instead of removing release artifacts and
uploading new ones, since removing old artifacts would require a new job
that all other jobs depend on to avoid re-removing, and would also
create a gap while CI is running run where no artifact is available.

We could upload artifacts using actions/upload-artifact in each job then
download them at the end and update the release at that point too, if we
really want to keep sha name in the nightly release artifacts. I don't
see much value of having the sha in the filename though.

.github/workflows/build-test-deploy.yaml

@@ -261,7 +261,7 @@ jobs:
           prerelease: true
           replacesArtifacts: true
           token: ${{ secrets.GITHUB_TOKEN }}
-          artifacts: "qTox-*.x86_64.AppImage,qTox-*.x86_64.AppImage.zsync"
+          artifacts: "qTox-nightly.x86_64.AppImage,qTox-nightly.x86_64.AppImage.zsync"
   build-flatpak:
     name: Flatpak
     runs-on: ubuntu-latest