Use an environment variable for PHP version

.github/workflows/ci.yml

@@ -5,6 +5,9 @@ on:
     branches: [production]
   pull_request:
 
+env:
+  php_verion: 7.4
+
 jobs:
   install:
     runs-on: ubuntu-latest
@@ -29,7 +32,7 @@ jobs:
       - name: Setup PHP
         uses: shivammathur/setup-php@5d27b8f
         with:
-          php-version: 7.4
+          php-version: $php_version
           extensions: mbstring
           coverage: none
           tools: composer:v1
@@ -86,7 +89,7 @@ jobs:
       - name: Setup PHP
         uses: shivammathur/setup-php@5d27b8f
         with:
-          php-version: 7.4
+          php-version: $php_version
           extensions: mbstring
           coverage: none
           tools: composer:v1
@@ -126,7 +129,7 @@ jobs:
       - name: Setup PHP
         uses: shivammathur/setup-php@5d27b8f
         with:
-          php-version: 7.4
+          php-version: $php_version
           tools: composer:v1
 
       - name: Install dependencies
@@ -158,7 +161,7 @@ jobs:
       - name: Setup PHP
         uses: shivammathur/setup-php@5d27b8f
         with:
-          php-version: 7.4
+          php-version: $php_version
           tools: composer:v1
 
       - name: Install dependencies