Fixed a bug with signing up a User instance

[cbaker6]

Creating a ParseUser instance, populating its properties, and using .signup resulted in the added properties for the ParseUser not being persisted to the Keychain on the client. All the data was saving to the server correctly.

Close #186

[codecov]

Codecov Report

Merging #187 (80dfa9d) into main (7af659b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #187   +/-   ##
=======================================
  Coverage   82.45%   82.45%           
=======================================
  Files          71       71           
  Lines        6749     6755    +6     
=======================================
+ Hits         5565     5570    +5     
- Misses       1184     1185    +1     

Impacted Files	Coverage Δ
Sources/ParseSwift/API/Responses.swift	90.47% <100.00%> (+1.90%)	⬆️
Sources/ParseSwift/Objects/ParseUser.swift	81.49% <100.00%> (-0.03%)	⬇️
Sources/ParseSwift/Objects/ParseObject.swift	77.39% <0.00%> (-0.27%)	⬇️

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