[wxfile] raise KeyError for non-existent keys.

[marscher]

Changes

WeldxFile now raises a KeyError, if a given key could not be accessed. Previously only a warning was emitted and the change was ignored. As this leads to confusion, e.g. None being returned, we now trigger the exception.

Related Issues

Closes #757

Checks

• updated CHANGELOG.rst
• updated tests

[github-actions]

Unit Test Results

       1 files  ±0         1 suites  ±0   3m 23s ⏱️ +48s
2 152 tests +7  2 152 ✔️ +7  0 💤 ±0  0 ❌ ±0 

Results for commit e51a5fe. ± Comparison against base commit 9af804a.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Merging #759 (e51a5fe) into master (9af804a) will increase coverage by 0.09%.
The diff coverage is 91.66%.

❗ Current head e51a5fe differs from pull request most recent head e6c465d. Consider uploading reports for the commit e6c465d to get more accurate results

@@            Coverage Diff             @@
##           master     #759      +/-   ##
==========================================
+ Coverage   96.76%   96.86%   +0.09%     
==========================================
  Files          88       88              
  Lines        6006     6005       -1     
==========================================
+ Hits         5812     5817       +5     
+ Misses        194      188       -6     

Impacted Files	Coverage Δ
weldx/asdf/file.py	96.20% <ø> (ø)
weldx/asdf/util.py	92.13% <91.66%> (+1.85%)	⬆️

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[CagtayFabry]

thank you for adding the test cases