GH Actions: version update for various predefined actions

A number of predefined actions have had major release, which warrant an update the workflow(s).

These updates don't actually contain any changed functionality, they are mostly just a change of the Node version used by the action itself (from Node 14 to Node 16).

Refs:
* https://github.com/actions/checkout/releases
* https://github.com/actions/upload-artifact/releases

php/doc-en@971e603

Author: mumumu

.github/workflows/integrate.yaml

@@ -21,20 +21,20 @@ jobs:
 
     steps:
       - name: "Checkout php/doc-${{ matrix.language }}"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v3"
         with:
           path: "${{ matrix.language }}"
           repository: "php/doc-${{ matrix.language }}"
 
       - name: "Checkout php/doc-en as fallback"
         if: "matrix.language != 'en'"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v3"
         with:
           path: "en"
           repository: "php/doc-en"
 
       - name: "Checkout php/doc-base"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v3"
         with:
           path: "doc-base"
           repository: "php/doc-base"