Added yaml.safe_load instead of yaml.load

[mstfbl]

This PR fixes an issue pointed out by Bandit w.r.t. using yaml.load, where it'd allow for unsafe loading of arbitrary objects, by using yaml.safe_load instead.

Bandit output:

>> Issue: [B506:yaml_load] Use of unsafe yaml load. Allows instantiation of arbitrary objects. Consider yaml.safe_load().
   Severity: Medium   Confidence: High
   Location: ./.circleci/utils/test_sort_yaml.py:14
   More Info: https://bandit.readthedocs.io/en/latest/plugins/b506_yaml_load.html
13	
14	sys.stdout.write(yaml.dump(yaml.load(sys.stdin, Loader=yaml.FullLoader), sort_keys=True))

[codecov]

Codecov Report

Merging #1278 (dbd8538) into master (803651c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1278   +/-   ##
=======================================
  Coverage   78.80%   78.80%           
=======================================
  Files          67       67           
  Lines        3624     3624           
=======================================
  Hits         2856     2856           
  Misses        768      768           

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