tests/main/snap-info: use yaml.safe_load rather than yaml.load

[bboozzoo]

Update the test script to work correctly with latest releases of PyYAML, which
now require the Loader to be passed for non-safe load() functions, like so:

+ python3 check.py
Traceback (most recent call last):
  File "check.py", line 70, in <module>
    res = list(yaml.load_all(sys.stdin))
TypeError: load_all() missing 1 required positional argument: 'Loader'

[mvo5]

Thank you

[mardy]

LGTM!

[codecov-commenter]

Codecov Report

Merging #11243 (e3b0c1f) into master (9cbabd6) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #11243   +/-   ##
=======================================
  Coverage   78.33%   78.33%           
=======================================
  Files         924      924           
  Lines      105374   105374           
=======================================
+ Hits        82545    82549    +4     
+ Misses      17688    17686    -2     
+ Partials     5141     5139    -2     

Flag	Coverage Δ
unittests	78.33% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/snap/cmd_debug_state.go	70.18% <0.00%> (-0.46%)	⬇️
overlord/hookstate/hookmgr.go	75.32% <0.00%> (+0.64%)	⬆️
osutil/synctree.go	79.24% <0.00%> (+2.83%)	⬆️

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