Remove quotes

In the case of a pull request made from a fork, secrets are not
accessible, and this resolved to null.
The codecov action seems to interpret null as no secret provided, while
it interprets the empty string as an invalid token, making the whole
tokenless upload invalid.

workflow-templates/continuous-integration.yml

@@ -27,7 +27,7 @@ jobs:
     with:
       php-versions: '["6.0", "6.1"]' # Use custom versions of PHP
     secrets:
-      CODECOV_TOKEN: "${{ secrets.CODECOV_TOKEN }}"
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
   phpunit-unstable-symfony:
     name: "PHPUnit with unstable Symfony"
@@ -39,4 +39,4 @@ jobs:
       # If the package requires some components but does not allow that version yet
       extra-requirements: "symfony/framework-bundle 47.1.x symfony/console 47.1.x"
     secrets:
-      CODECOV_TOKEN: "${{ secrets.CODECOV_TOKEN }}"
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}