fix: Allow action field decorators without makeObservable (#3879)

[Obi-Dann]

Code change checklist

• [x] Added/updated unit tests
• [ ] N/A ~Updated /docs. For new functionality, at least API.md should be updated~
• [x] Verified that there is no significant performance drop (yarn mobx test:performance)

fixes #3879

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 289e8746a201ed026eebb08180d9c94d666f4d29

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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mobx	Patch

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[jzhan-canva]

can we merge this PR?

[Matchlighter]

Closing in favor of https://github.com/mobxjs/mobx/pull/3902