fix(store): allow a generic reducer

[timdeschryver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #2982

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

While this works, I can't explain why ...😅

[alex-okrushko]

while this works, I can't explain why ...😅

😂😂😂

[alex-okrushko]

Suggested change

	const reducer = args.pop() as OnReducer<any, Creators>;
	const reducer = args.pop() as OnReducer<unknown, Creators>;

Would that still work? 🙂