ci(PHP 8.0): add CI processes for PHP 8.0

CI environment for the PHP 8.0 should be implemented.

Closes laradock#2863

.github/workflows/main-ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php_version: ["7.1", "7.2", "7.3", "7.4"]
+        php_version: ["7.1", "7.2", "7.3", "7.4", "8.0"]
         service: [php-fpm, php-worker, workspace, laravel-horizon]
     steps:
     - uses: actions/checkout@v2

.travis.yml

@@ -13,13 +13,15 @@ env:
     - PHP_VERSION=7.2 BUILD_SERVICE=workspace
     - PHP_VERSION=7.3 BUILD_SERVICE=workspace
     - PHP_VERSION=7.4 BUILD_SERVICE=workspace
+    - PHP_VERSION=8.0 BUILD_SERVICE=workspace
 
     - PHP_VERSION=5.6 BUILD_SERVICE=php-fpm
     - PHP_VERSION=7.0 BUILD_SERVICE=php-fpm
     - PHP_VERSION=7.1 BUILD_SERVICE=php-fpm
     - PHP_VERSION=7.2 BUILD_SERVICE=php-fpm
     - PHP_VERSION=7.3 BUILD_SERVICE=php-fpm
     - PHP_VERSION=7.4 BUILD_SERVICE=php-fpm
+    - PHP_VERSION=8.0 BUILD_SERVICE=php-fpm
 
     - PHP_VERSION=hhvm BUILD_SERVICE=hhvm
 
@@ -29,12 +31,14 @@ env:
     - PHP_VERSION=7.2 BUILD_SERVICE=php-worker
     - PHP_VERSION=7.3 BUILD_SERVICE=php-worker
     - PHP_VERSION=7.4 BUILD_SERVICE=php-worker
+    - PHP_VERSION=8.0 BUILD_SERVICE=php-worker
 
     - PHP_VERSION=7.0 BUILD_SERVICE=laravel-horizon
     - PHP_VERSION=7.1 BUILD_SERVICE=laravel-horizon
     - PHP_VERSION=7.2 BUILD_SERVICE=laravel-horizon
     - PHP_VERSION=7.3 BUILD_SERVICE=laravel-horizon
     - PHP_VERSION=7.4 BUILD_SERVICE=laravel-horizon
+    - PHP_VERSION=8.0 BUILD_SERVICE=laravel-horizon
 
     - PHP_VERSION=NA BUILD_SERVICE=solr
     - PHP_VERSION=NA BUILD_SERVICE="mssql rethinkdb aerospike"