Update action to use upload-artifact v4

GitHub announced that v3 of actions/upload-artifact is EOL and would start brownouts
on November 14th. This small change moves to v4 of this action.

Author: petetronic

.github/actions/build-vsix/action.yml

@@ -87,7 +87,7 @@ runs:
       shell: bash
 
     - name: Upload VSIX
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: ${{ inputs.artifact_name }}
         path: ${{ inputs.vsix_name }}