SVG stroke-width with explicit unit, fixes #526

[gmischler]

e.g. Fixes #526

Checklist:

• The GitHub pipeline is OK (green),
  meaning that both pylint (static code analyzer) and black (code formatter) are happy with the changes of this PR.
• A unit test is covering the code added / modified by this PR
• This PR is ready to be merged
• [NA] In case of a new feature, docstrings have been added, with also some documentation in the docs/ folder
• A mention of the change is present in CHANGELOG.md

By submitting this pull request, I confirm that my contribution is made under the terms of the GNU LGPL 3.0 license.

[codecov]

Codecov Report

Merging #542 (8ddd5b7) into master (54b0309) will decrease coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #542      +/-   ##
==========================================
- Coverage   94.10%   93.97%   -0.13%     
==========================================
  Files          22       22              
  Lines        6206     6073     -133     
  Branches     1265     1232      -33     
==========================================
- Hits         5840     5707     -133     
  Misses        191      191              
  Partials      175      175              

Impacted Files	Coverage Δ
fpdf/svg.py	95.94% <100.00%> (+0.02%)	⬆️
fpdf/prefs.py	90.90% <0.00%> (-1.95%)	⬇️
fpdf/drawing.py	92.73% <0.00%> (-0.28%)	⬇️
fpdf/syntax.py	95.37% <0.00%> (-0.05%)	⬇️
fpdf/fpdf.py	92.56% <0.00%> (-0.01%)	⬇️
fpdf/sign.py	100.00% <0.00%> (ø)
fpdf/enums.py	100.00% <0.00%> (ø)
fpdf/__init__.py	100.00% <0.00%> (ø)

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[Lucas-C]

👍 Perfect PR!
Thank you @gmischler