test: improve localhost connections

[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

Arbitrary loads should only be enabled for localhost when testing.

Related issue: #n/a

Approach

Improve the way TestHost's connect to localhost during testing.

TODOs before merging

• [x] Add changes to documentation (guides, repository pages, in-code descriptions)

[parse-github-assistant[bot]]

Thanks for opening this pull request!

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

[codecov[bot]]

Codecov Report

Merging #336 (ddd8311) into main (879055b) will increase coverage by 0.09%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #336      +/-   ##
==========================================
+ Coverage   85.10%   85.20%   +0.09%     
==========================================
  Files         114      114              
  Lines       12208    12208              
==========================================
+ Hits        10390    10402      +12     
+ Misses       1818     1806      -12     

Impacted Files	Coverage Δ
Sources/ParseSwift/Objects/ParseUser+async.swift	100.00% <ø> (ø)
Sources/ParseSwift/Objects/ParseUser+combine.swift	95.55% <ø> (ø)
Sources/ParseSwift/Objects/ParseUser.swift	83.18% <ø> (ø)
Sources/ParseSwift/Objects/ParseObject.swift	82.74% <0.00%> (+0.45%)	:arrow_up:
Sources/ParseSwift/LiveQuery/ParseLiveQuery.swift	74.26% <0.00%> (+1.33%)	:arrow_up:

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