Fix: Use magic methods instead of magic properties

[localheinz]

This pull request

• uses magic methods instead of deprecated magic properties

Follows #434.

[codecov]

Codecov Report

Merging #435 (21c6d2f) into main (4a77eb6) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 21c6d2f differs from pull request most recent head 4d6ee9c. Consider uploading reports for the commit 4d6ee9c to get more accurate results

@@             Coverage Diff             @@
##                main      #435   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        87        87           
===========================================
  Files             12        12           
  Lines            302       302           
===========================================
  Hits             302       302           

Impacted Files	Coverage Δ	Complexity Δ
src/DataProvider/StringProvider.php	100.00% <100.00%> (ø)	12.00 <0.00> (ø)

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