Bump yaml in tests to 6.0+ and switch to safe_load

[mahmoud]

Fixes tox under py310. Also safer!

[codecov[bot]]

Codecov Report

Merging #262 (db3f11b) into master (c97b71a) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #262   +/-   ##
=======================================
  Coverage   98.01%   98.01%           
=======================================
  Files          27       27           
  Lines        4335     4335           
  Branches      748      748           
=======================================
  Hits         4249     4249           
  Misses         56       56           
  Partials       30       30           

Files Changed	Coverage Δ
glom/cli.py	85.82% <100.00%> (ø)

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