docs: Fix various typos in main/

Found via `codespell -q 3 -S "./CREDITS" -L abd,asent,atleast,childrens,contentn,crypted,dne,durationm,exten,inout,leapyear,nd,oclock,offsetp,ot,parm,parms,requestor,ser,slanguage,slin,thirdparty,varn,varns,ues`

main/json.c

@@ -88,7 +88,7 @@ enum ast_json_type ast_json_typeof(const struct ast_json *json)
 	case JSON_FALSE: return AST_JSON_FALSE;
 	case JSON_NULL: return AST_JSON_NULL;
 	}
-	ast_assert(0); /* Unexpect return from json_typeof */
+	ast_assert(0); /* Unexpected return from json_typeof */
 	return r;
 }