adapt to toggleableActiveColor property having been deprecated

adapt to toggleableActiveColor property having been deprecated

ThemeData's toggleableActiveColor property has been deprecated [0].
This fix was done by `dart fix --apply` and thus is naturally a
relative broad automatic fix where we might only require a subset
from, but for now just trust the linter to do the safe thing.

[0]: https://docs.flutter.dev/release/breaking-changes/toggleable-active-color

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>