Update GH actions: Add composer update and validate steps

Author: SerafimArts

Diff for: .github/workflows/main.yml

@@ -29,6 +29,10 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
+      - name: Update Composer
+        run: composer self-update
+      - name: Validate Composer Config
+        run: composer validate
       - name: Get Composer Cache Directory
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"
@@ -66,6 +70,10 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
+      - name: Update Composer
+        run: composer self-update
+      - name: Validate Composer Config
+        run: composer validate
       - name: Get Composer Cache Directory
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"
@@ -109,6 +117,10 @@ jobs:
           tools: pecl
           ini-values: "memory_limit=-1"
           extensions: phar, ffi
+      - name: Update Composer
+        run: composer self-update
+      - name: Validate Composer Config
+        run: composer validate
       - name: Get Composer Cache Directory
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"