[DataGrid] Prevent paste operations in non-editable cells (#11984)

[ikzhr]

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Description

Fixes #11984

• When pasting, only the column's editable property was being referenced, but now the isCellEditable prop is also taken into consideration.

Test results

The table below shows which cells can be overwritten with paste

	isCellEditable prop returns true	isCellEditable prop returns false
colDef.editable is true	:o:	:x: (:o: before the fix)
colDef.editable is false	:x:	:x:

:o: : Can paste, :x: : Can not paste

[mui-bot]

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[arminmeh]

Thanks for the contribution @ikzhr Would you mind adding a small test for this fix? Also, can you rebase with the latest master branch?

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[github-actions[bot]]

This pull request has been closed due to 15 days of inactivity after being marked stale.