fix: dependencies in c7n-mailer

[manheim-tooling]

Description

• Updates the dependencies for c7n-mailer
• Updates the sphinx dependencies

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[codecov-commenter]

Codecov Report

Merging #75 (8d94847) into master (ae3c803) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #75   +/-   ##
=======================================
  Coverage   61.49%   61.49%           
=======================================
  Files           9        9           
  Lines        1470     1470           
  Branches      306      306           
=======================================
  Hits          904      904           
  Misses        565      565           
  Partials        1        1           

Impacted Files	Coverage Δ
manheim_c7n_tools/version.py	100.00% <100.00%> (ø)

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