Fix issue with mutable dataclass fields.

[mcmtroffaes]

Closes #284.

@jamesjer I'll wait for CI to cycle and perhaps add 3.11 to the github actions; if all is well this should be good to go. Feel free to give this a spin. Thanks again for your help with this!

[codecov]

Codecov Report

Merging #285 (3c9bdd3) into develop (a8b9010) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 3c9bdd3 differs from pull request most recent head a2f71d9. Consider uploading reports for the commit a2f71d9 to get more accurate results

@@            Coverage Diff             @@
##           develop      #285    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           47        47            
  Lines         2290      2301    +11     
  Branches       278       403   +125     
==========================================
+ Hits          2290      2301    +11     

Impacted Files	Coverage Δ
...sphinxcontrib/bibtex/style/referencing/__init__.py	100.00% <100.00%> (ø)
...inxcontrib/bibtex/style/referencing/author_year.py	100.00% <100.00%> (ø)
...trib/bibtex/style/referencing/basic_author_year.py	100.00% <100.00%> (ø)
...hinxcontrib/bibtex/style/referencing/basic_foot.py	100.00% <100.00%> (ø)
...inxcontrib/bibtex/style/referencing/basic_label.py	100.00% <100.00%> (ø)
...inxcontrib/bibtex/style/referencing/basic_super.py	100.00% <100.00%> (ø)
...nxcontrib/bibtex/style/referencing/extra_author.py	100.00% <100.00%> (ø)
...inxcontrib/bibtex/style/referencing/extra_empty.py	100.00% <100.00%> (ø)
...inxcontrib/bibtex/style/referencing/extra_label.py	100.00% <100.00%> (ø)
...hinxcontrib/bibtex/style/referencing/extra_year.py	100.00% <100.00%> (ø)
... and 8 more

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