fix: task expected type string, got bool

[wallberg]

Summary of changes

Fixed Taskfile.yml in several places where a variable was provided
as type bool, but string was expected, causing task to fail to
execute, for example:

$ task lint
task: Failed to run task "lint": template: :1:63: executing "" at <"false">: wrong type for value; expected string; got bool

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• tests are passing; lint and mypy are not passing
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.