Fix ambiguity with new mul! methods in Julia v1.7

[blegat]

New mul! methods were added in JuliaLang/julia#29634 so we now have to add methods to fix ambiguities.

[codecov]

Codecov Report

Merging #127 (61dbe44) into master (c4c2e7a) will decrease coverage by 1.07%.
The diff coverage is 26.66%.

@@            Coverage Diff             @@
##           master     #127      +/-   ##
==========================================
- Coverage   86.23%   85.15%   -1.08%     
==========================================
  Files          20       20              
  Lines        1765     1785      +20     
==========================================
- Hits         1522     1520       -2     
- Misses        243      265      +22     

Impacted Files	Coverage Δ
src/dispatch.jl	53.29% <26.66%> (-7.94%)	⬇️
src/rewrite.jl	80.61% <0.00%> (-0.52%)	⬇️

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