Stores: fix overwriting underscore property

[morethanwords]

Summary

Store doesn't handle _ property well. It works fine when adding element first time, but when you try to modify the same element, property will be undefined.

How did you test this change?

pnpm t

[changeset-bot]

🦋 Changeset detected

Latest commit: 26b1d48

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

This PR includes changesets to release 2 packages

Name	Type
solid-js	Patch
test-integration	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[ryansolid]

Thank you.

[coveralls]

Pull Request Test Coverage Report for Build 5800790021

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.003%) to 93.913%

---

Files with Coverage Reduction	New Missed Lines	%
packages/solid/src/index.ts	1	97.87%

Totals
Change from base Build 5756852867:	0.003%
Covered Lines:	4142
Relevant Lines:	4343

---

💛 - Coveralls