Update explanation of job-level variable override to fit example

doc/ci/variables/README.md

@@ -120,7 +120,7 @@ The YAML-defined variables are also set to all created
 tune them.
 
 Variables can be defined at a global level, but also at a job level. To turn off
-global defined variables in your job, define an empty array:
+global defined variables in your job, define an empty hash:
 
 ```yaml
 job_name:

doc/ci/yaml/README.md

@@ -434,7 +434,7 @@ but allows you to define job-specific variables.
 
 When the `variables` keyword is used on a job level, it overrides the global YAML
 job variables and predefined ones. To turn off global defined variables
-in your job, define an empty array:
+in your job, define an empty hash:
 
 ```yaml
 job_name: