Fix compilation issue on LTS due to changes in NearestNeighbors (NN) API

[tpoisot]

What the pull request does
A change in NL (always_false as an export was replaced by Returns(false) broke precompilation.

Fixes #76

This has been fixed by creating a global variable always_false = Returns(false). If NN exports always_false, this one is used instead. The later is important as previous versions of NN may not handle Returns(false). This results in no change to the package code.

Type of change

• 🐛 Bug fix (non-breaking change which fixes an issue)

Checklist

• The changes are tested
• The changes do not modify the behavior of the previously existing functions
• The Project.toml field version has been updated

[tpoisot]

@mkborregaard I've also brought the julia github actions to their latest versions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.39%. Comparing base (db77779) to head (091fa10).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #77      +/-   ##
==========================================
+ Coverage   88.23%   88.39%   +0.15%     
==========================================
  Files          19       19              
  Lines         476      491      +15     
==========================================
+ Hits          420      434      +14     
- Misses         56       57       +1     

Flag	Coverage Δ
unittests	88.39% <ø> (+0.15%)	⬆️

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[tpoisot]

@mkborregaard - just a bump, this is ready to merge afaict

[mkborregaard]

Sorry, I had missed this!