fix: add 5.1 SPM file

[cbaker6]

New Pull Request Checklist

• [x] I am not disclosing a vulnerability.
• [x] I am creating this PR in reference to an issue.

Issue Description

Add SPM 5.1 file for older systems.

Related issue: #n/a

Approach

Same Package file with older tools before bumping to Swift 5.5

TODOs before merging

• [x] Ensure CI passes

[parse-github-assistant[bot]]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[codecov[bot]]

Codecov Report

Merging #337 (19fcf6c) into main (4187847) will increase coverage by 0.05%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #337      +/-   ##
==========================================
+ Coverage   85.10%   85.16%   +0.05%     
==========================================
  Files         114      114              
  Lines       12208    12208              
==========================================
+ Hits        10390    10397       +7     
+ Misses       1818     1811       -7     

Impacted Files	Coverage Δ
Sources/ParseSwift/Objects/ParseObject.swift	82.74% <0.00%> (+0.45%)	:arrow_up:
Sources/ParseSwift/LiveQuery/ParseLiveQuery.swift	73.52% <0.00%> (+0.59%)	:arrow_up:

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