Use tuple for pip constraints to avoid LRU cache error

[jni]

The _pip_constraints function was returning a list of strings, but the function that required it was decorated with lru_cache, causing an error because list is not hashable. See https://forum.image.sc/t/request-for-testing-napari-0-4-18-release-candidate/82833/21.

Type of change

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

[jni]

@jaimergp once again — I'm so grateful for the work you've done pulling out this installer 😭 🙏

[codecov]

Codecov Report

Merging #6036 (c611d7a) into v0.4.18x (c858b57) will decrease coverage by 0.04%.
The diff coverage is 0.00%.

❗ Current head c611d7a differs from pull request most recent head cf983c1. Consider uploading reports for the commit cf983c1 to get more accurate results

@@             Coverage Diff              @@
##           v0.4.18x    #6036      +/-   ##
============================================
- Coverage     88.71%   88.68%   -0.04%     
============================================
  Files           624      624              
  Lines         52781    52779       -2     
============================================
- Hits          46825    46805      -20     
- Misses         5956     5974      +18     

Impacted Files	Coverage Δ
napari/_qt/dialogs/qt_plugin_dialog.py	61.91% <0.00%> (+0.03%)	⬆️

... and 9 files with indirect coverage changes