Clarify `environment` docs.

The object is not used only for tests, but also for `custom_target` etc.

docs/yaml/objects/env.yaml

@@ -2,9 +2,8 @@ name: env
 long_name: Environment
 description: |
   This object is returned by [[environment]] and stores
-  detailed information about how environment variables should be set
-  during tests. It should be passed as the `env` keyword argument to
-  tests and other functions.
+  detailed information about how environment variables should be set.
+  It should be passed as the `env` keyword argument to tests and other functions.
 
   *Since 0.58.0* [[env.append]] and [[env.prepend]] can be called multiple times
   on the same `varname`. Earlier Meson versions would warn and only the last