Update to actions/upload-artifact@v4

Author: ice-phoenix

.github/actions/upload-spec-artifacts/action.yml

@@ -3,13 +3,13 @@ runs:
   using: 'composite'
   steps:
     - name: 'Upload Kotlin spec PDF artifacts'
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: kotlin-spec-pdf
         path: |
           build/spec/pdf/
     - name: 'Upload Kotlin spec HTML artifacts'
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: kotlin-spec-html
         path: |