Use overloads while passing culture

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
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• I have provided test coverage for my change (where applicable)

Description

Roslyn is incorrectly flagging CA1304 against the codebase following the move to .NET 6. I can't stop it doing that but I did find areas where we were not using the overloads correctly in our FontCollection based types.
354

[codecov]

Codecov Report

Merging #359 (429d527) into main (a70c2be) will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##            main    #359   +/-   ##
=====================================
  Coverage     86%     86%           
=====================================
  Files        238     238           
  Lines      15171   15171           
  Branches    2100    2100           
=====================================
  Hits       13073   13073           
  Misses      1613    1613           
  Partials     485     485           

Flag	Coverage Δ
unittests	86% <100%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
src/SixLabors.Fonts/FontCollection.cs	88% <100%> (ø)
src/SixLabors.Fonts/SystemFontCollection.cs	52% <100%> (ø)
src/SixLabors.Fonts/SystemFonts.cs	100% <100%> (ø)

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