Make task-lists-elements CSP Trusted Types compatible

[KyFaSt]

This change makes task-lists-elements compatible with the CSP directive Trusted Types. This CSP directive allows developers to mark a value as a Trusted Type, usually this would be done in conjunction with running some type of sanitizer like DOMPurify to ensure the value doesn't contain any unsafe elements. Fortunately, task-lists-elements doesn't have major violations, just this one. Unfortunately the change in this PR does not buy any security benefits, it just adheres to the Trusted Types API -- not passing bare strings directly to potentially dangerous injection sinks. Currently this implementation is the best way to make this library compatible with trusted types.

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[fletchto99]

Looks good from a pse-architecture perspective! Its unfortunate we need to be so verbose for something like this but unfortunately we have no way to indicate that an innerHTML is coming from a hardcoded string 😓