Recognise both byte and string object for NXdata tag in NeXus reader

[ptim0626]

This PR (originally hyperspy/hyperspy#3137) is a small improvement on the NeXus reader, allowing it to recognise NXdata tag as both byte and string object. This increases flexibility and avoid missing genuine NXdata dataset when its tag is saved as a string object.

Progress of the PR

• Change implemented (can be split into several points),
• add an changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• add test,
• ready for review.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.05 🎉

Comparison is base (85918a4) 85.20% compared to head (05f24b0) 85.26%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
+ Coverage   85.20%   85.26%   +0.05%     
==========================================
  Files          73       73              
  Lines        8991     9030      +39     
  Branches     2030     2045      +15     
==========================================
+ Hits         7661     7699      +38     
  Misses        871      871              
- Partials      459      460       +1     

Impacted Files	Coverage Δ
rsciio/nexus/_api.py	91.63% <100.00%> (ø)

... and 3 files with indirect coverage changes

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[ericpre]

Could you please add a test?

[ptim0626]

Could you please add a test?
Yes it is done now.

[ericpre]

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