bump: rust 1.55

[baszalmstra]

A simple bump of Rust to 1.55

[codecov]

Codecov Report

Merging #350 (735312b) into main (94ffbb2) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #350      +/-   ##
==========================================
- Coverage   80.11%   80.10%   -0.01%     
==========================================
  Files         261      261              
  Lines       15703    15697       -6     
==========================================
- Hits        12580    12574       -6     
  Misses       3123     3123              

Impacted Files	Coverage Δ
crates/mun_abi/src/test_utils.rs	100.00% <0.00%> (ø)

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