Fixed typo (“at an offset”, not “at in offset”). (#1771)

Author: wadetregaskis

proposals/0369-add-customdebugdescription-conformance-to-anykeypath.md

@@ -104,7 +104,7 @@ The new debugging output will not be backdeployed, so Swift programs running on
 The implementation of `debugDescription` might change after the initial work to implement this proposal is done. In particular, the output format will not be guaranteed to be stable. Here are a few different changes we might anticipate making: 
 
 - As new features are added to the compiler, there may be new metadata available in the binary to draw from. One example would be lookup tables of KeyPath segment to human-readable-name or some other unique, stable identifier
-- Whenever a new feature is added to `KeyPath`, it will need to be reflected in the output of this function. For example, the `KeyPath`s produced by [\_forEachFieldWithKeyPath](https://github.com/apple/swift/blob/main/stdlib/public/core/ReflectionMirror.swift#L324) are incomplete, in the sense that they merely set a value at in offset in memory and do not call `didSet` observers. If this function were ever publicly exposed, it would be useful if this was surfaced in the debugging information. 
+- Whenever a new feature is added to `KeyPath`, it will need to be reflected in the output of this function. For example, the `KeyPath`s produced by [\_forEachFieldWithKeyPath](https://github.com/apple/swift/blob/main/stdlib/public/core/ReflectionMirror.swift#L324) are incomplete, in the sense that they merely set a value at an offset in memory and do not call `didSet` observers. If this function were ever publicly exposed, it would be useful if this was surfaced in the debugging information. 
 - The behavior of subscript printing might be changed: for example, we might always print out the value of the argument to the subscript, or we might do so only in cases where the output is short. We might also change from `.subscript()` to `[]`
 - The Swift language workgroup may create new policies around debug descriptions and the output of this function might need to be updated to conform to them