workflows/release-tasks: Fix missing suffix on doxygen tarballs

[dim]

Is the -srcdir option no longer needed?

[tstellar]

In D145997#4191168, @dim wrote:

Is the -srcdir option no longer needed?

Yes, the -release option will download the tarball from github and build the docs from that instead of the current checkout (which is what -srcdir does).

.github/workflows/release-tasks.yml

steps:
         uses: actions/checkout@v3
 
       - name: Create Release
         run: |
           ./llvm/utils/release/./github-upload-release.py --token ${{ github.token }} --release ${{ steps.validate-tag.outputs.release-version }} create
 
       - name: Build Documentation
         run: |
-          ./llvm/utils/release/build-docs.sh -srcdir llvm
+          ./llvm/utils/release/build-docs.sh -release ${{ steps.validate-tag.outputs.release-version }}
           ./llvm/utils/release/github-upload-release.py --token ${{ github.token }} --release ${{ steps.validate-tag.outputs.release-version }} upload --files *doxygen*.tar.xz
 
       - name: Create Release Notes Artifact
         uses: actions/download-artifact@v1
         with:
           name: release-notes
           path: docs-build/html-export/