Use node 15 for build devextreme package (#629)

* Update node to 15 version

* Use 14 node after devextreme build

Author: alexanderPolosatov

.github/workflows/tests.yml

@@ -26,6 +26,11 @@ jobs:
     - name: Clone devextreme repo
       run: test -d ../devextreme-repo || git clone -b 21_2 https://github.com/devexpress/devextreme ../devextreme-repo
 
+    - name: Use Node.js 15
+      uses: actions/setup-node@v2
+      with:
+        node-version: '15'
+
     - name: Install packages in devextreme repo
       run: |
         cd ../devextreme-repo
@@ -34,6 +39,10 @@ jobs:
       run: |
         cd ../devextreme-repo
         npm run build-dist
+    - name: Use Node.js 14
+      uses: actions/setup-node@v2
+      with:
+        node-version: '14'
     - name: Install devextreme package
       run: |
         cd ./packages/devextreme-react