Let ansible-lint check Jinja syntax in role tasks again

The skip list has disabled no-jinja-nesting since 2022. ansible-lint
v6.6.0 replaced that rule with jinja[invalid], and ansible-lint still
maps the old name to it, so the skip now turns off the Jinja syntax
check for tasks in roles/custom, the only path the ansible-lint hook
lints. Remove the skip.

roles/custom has no jinja[invalid] findings at this commit. A syntax
error planted in a task's arguments is reported with this change and
not without it; one planted in a role's defaults file is not reported
either way.

.config/ansible-lint.yml

@@ -9,7 +9,6 @@ use_default_rules: true
 skip_list:
   - unnamed-task
   - no-handler
-  - no-jinja-nesting
   - schema
   - command-instead-of-shell
   - role-name