fix: Use chmod inside the CCACHE directory

If we need to replace the docker image for any reason, the user will
(probably) be different. This ensures that the CCACHE directory can be
read and writen by any user of the docker image being used in the CI.

.gitlab-ci.yml

@@ -37,6 +37,7 @@ build-linux:
       - $CACHE_DIR
   before_script:
     - mkdir -p $CACHE_DIR
+    - chmod -R 777 $CACHE_DIR
     - ls -la $CACHE_DIR
   variables:
     GIT_SUBMODULE_STRATEGY: recursive