Ensure template_path always uses "/" to match jinja

[cb160]

This PR shoudl fix #1545

The existing code substituted / for , assuming this was the right behaviour for windows. But on Windows, Jinja still uses / for the template list - See https://github.com/pallets/jinja/blob/896a62135bcc151f2997e028c5125bec2cb2431f/src/jinja2/loaders.py#L225

[codecov]

Codecov Report

Merging #1617 (af293c9) into main (2aa686c) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1617      +/-   ##
==========================================
+ Coverage   92.09%   92.16%   +0.06%     
==========================================
  Files          34       34              
  Lines        4518     4531      +13     
==========================================
+ Hits         4161     4176      +15     
+ Misses        357      355       -2     

Impacted Files	Coverage Δ
datasette/app.py	95.37% <100.00%> (ø)
datasette/views/table.py	96.19% <0.00%> (ø)
datasette/utils/__init__.py	94.79% <0.00%> (+<0.01%)	⬆️
datasette/views/base.py	95.49% <0.00%> (+0.07%)	⬆️
datasette/views/special.py	95.09% <0.00%> (+2.38%)	⬆️

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[simonw]

Aha I understand the problem now! pallets/jinja#1378 (comment)

Jinja template names/paths are not always filesystem paths. So regardless of the OS Jinja always uses forward slashes.

[simonw]

I was hoping to get the test suite running on Windows before merging this PR but that looks like it will be a BIG job, see:

• Get the tests passing against Windows #1627

So I'm going to merge this one as-is for the moment.