Fix typos in the Data Race Safety section (#121)

* Fix spelling of "access"

* Add missing "of"

Author: jasonhawkins

Guide.docc/DataRaceSafety.md

@@ -493,8 +493,8 @@ func populate(island: Island, with chicken: sending Chicken) async {
 ```
 
 The compiler can now provide the guarantee that at all call sites, the
-`chicken` parameter will never be subject to unsafe acceses.
-This is a relaxing an otherwise significant constraint.
+`chicken` parameter will never be subject to unsafe access.
+This is a relaxing of an otherwise significant constraint.
 Without `sending`, this function would only be possible to implement by
 requiring that `Chicken` first conform to `Sendable`.