chore #933 Make CI great again (jakubtobiasz)

This PR was merged into the 1.12 branch.

Discussion
----------

For an unknown reason Sylius-Standard installs Sylius `1.12.9` on CI instead of the latest `1.12.11`. I precised the minimal version to `^1.12.11` so it should work fine.

Commits
-------
  Bump minimal sylius/sylius version
  Remove the Docker build in CI
  Update auto-merge workflow's OS version

.github/workflows/auto-merge.yml

@@ -5,7 +5,7 @@ on:
 
 jobs:
     auto-merge:
-        runs-on: ubuntu-18.04
+        runs-on: ubuntu-20.04
         steps:
             -
                 name: Checkout repository

composer.json

@@ -26,7 +26,7 @@
     "require": {
         "php": "^8.0",
         "sylius/paypal-plugin": "^1.5",
-        "sylius/sylius": "^1.12",
+        "sylius/sylius": "^1.12.11",
         "symfony/dotenv": "^5.4 || ^6.0",
         "symfony/runtime": "^5.4 || ^6.0",
         "symfony/flex": "^2.1"