BF: When download-url gets Pathobject as path convert it to a string

[adswa]

Tiny fix for #6090

[codecov]

Codecov Report

Merging #6317 (6b74c84) into master (2b92a76) will decrease coverage by 37.60%.
The diff coverage is 100.00%.

❗ Current head 6b74c84 differs from pull request most recent head 860bb4f. Consider uploading reports for the commit 860bb4f to get more accurate results

@@             Coverage Diff             @@
##           master    #6317       +/-   ##
===========================================
- Coverage   89.87%   52.27%   -37.61%     
===========================================
  Files         331      331               
  Lines       43210    43190       -20     
===========================================
- Hits        38835    22577    -16258     
- Misses       4375    20613    +16238     

Impacted Files	Coverage Δ
datalad/local/download_url.py	69.79% <100.00%> (-28.13%)	⬇️
datalad/version.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/wtf.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/addurls.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/tests/test_cmd.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/interface/clean.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/interface/rerun.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/__init__.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/no_annex.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/support/digests.py	0.00% <0.00%> (-100.00%)	⬇️
... and 229 more

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[adswa]

Just commenting to not let this PR become stale, but there is no urgency: This is ready for someone to look at, and a quick 4-character-change to approve or dismiss :)

[yarikoptic]

merged, and CPed (had to manually fix path since file moved)/pushed to maint (what could go wrong, right? ;)).
Although indeed resolves the issue, IMHO it is just a band-aid for a more general issue of our code (in particular Interfaces) in many places expecting paths to be passed as string not as Path object. May be in some bright future we would get more type annotations done to catch them in CI times