Some individuals may be sensitive to edits of their posts on the basis of spelling or grammar. Some editors may be concerned about what to put in as a reason/explanation for the edit. New editors, in general, are likely uncertain of what the accepted "etiquette" is, on these sites, for such corrections.
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Spelling and grammar corrections are acceptable - anything that improves a question is a good thing.
What you put in the summary is up to you - "Improved spelling/grammar" is an option.
Though the purpose of SO is not to teach English, helping people understand the edits and thus improve their English is a good thing - so your first option will have more benefit for the OP.