Pin rust nightly

[samuelcolvin]

Until rust-lang/rust#98833 is resolved

[codecov]

Codecov Report

Merging #145 (6156da3) into main (d3a6bf3) will not change coverage.
The diff coverage is n/a.

❗ Current head 6156da3 differs from pull request most recent head 6758521. Consider uploading reports for the commit 6758521 to get more accurate results

@@           Coverage Diff           @@
##             main     #145   +/-   ##
=======================================
  Coverage   97.45%   97.45%           
=======================================
  Files          41       41           
  Lines        4007     4007           
  Branches       28       28           
=======================================
  Hits         3905     3905           
  Misses        102      102           

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