minor #15018 [Internal] Set the specific version of the doc-builder (javiereguiluz)

This PR was submitted for the 5.x branch but it was squashed and merged into the 4.4 branch instead.

Discussion
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[Internal] Set the specific version of the doc-builder

We're going to do some changes in the doc-builder dependency, so let's pin its version to a specific commit to avoid any issues.

Commits
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c335d0e [Internal] Set the specific version of the doc-builder

Author: javiereguiluz

_build/composer.json

@@ -15,8 +15,8 @@
     },
     "require": {
         "php": ">=7.2.9",
-        "symfony/console": "^4.1",
-        "symfony/docs-builder": "dev-master",
-        "symfony/process": "9999999-dev"
+        "symfony/console": "^4.4",
+        "symfony/docs-builder": "^0.12.0",
+        "symfony/process": "^4.4"
     }
 }