fix: pdate ExecProvider to use safe_get()

[tomplus]

Sync with synchronous lib: kubernetes-client/python-base#91

[codecov-io]

Codecov Report

Merging #48 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
+ Coverage   94.37%   94.38%   +<.01%     
==========================================
  Files          20       20              
  Lines        1352     1353       +1     
==========================================
+ Hits         1276     1277       +1     
  Misses         76       76

Impacted Files	Coverage Δ
kubernetes_asyncio/config/exec_provider.py	96% <100%> (ø)	⬆️
kubernetes_asyncio/config/exec_provider_test.py	100% <100%> (ø)	⬆️

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