fix: Fix NU1009 reference assembly warning

[austindrenski]

Very silly, had this right in my internal projects and decided to "simplify" it when I reimplemented here 🤦🤦🤦

tldr; NuGet analyzers run over the Directory.Packages.props file without validating whether a given PackageVersion is used in a given TFM, so the analyzer pops even though the build is happy. I'm still a little confused as to why I can't repro locally, but probably caching, so "un-simplifying" my earlier oops and all should hopefully work as intended going forward.

See: #165, #196, #219, #220

H/T @CommCody

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (130654b) 93.50% compared to head (c2fb940) 93.50%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #222 +/- ## ======================================= Coverage 93.50% 93.50% ======================================= Files 23 23 Lines 954 954 Branches 105 105 ======================================= Hits 892 892 Misses 38 38 Partials 24 24 ```

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[austindrenski]

@CommCody please pull the latest main and let us know if you have any further build issues. Thanks again for reporting!

[CommCody]

@austindrenski I can confirm that main builds for me now