Fix panel serve index template

[philippjfr]

Fixes #3970

[codecov]

Codecov Report

Merging #3980 (181fc06) into master (0decd94) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3980   +/-   ##
=======================================
  Coverage   83.67%   83.68%           
=======================================
  Files         223      223           
  Lines       33039    33033    -6     
=======================================
- Hits        27645    27643    -2     
+ Misses       5394     5390    -4     

Flag	Coverage Δ
ui-tests	37.44% <28.57%> (+<0.01%)	⬆️
unitexamples-tests	74.82% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
panel/tests/test_server.py	99.80% <100.00%> (+<0.01%)	⬆️
panel/io/reload.py	69.56% <0.00%> (-2.18%)	⬇️
panel/tests/command/test_serve.py	83.95% <0.00%> (-1.42%)	⬇️
panel/io/state.py	69.41% <0.00%> (-0.17%)	⬇️
panel/tests/util.py	87.25% <0.00%> (-0.13%)	⬇️
panel/io/jupyter_server_extension.py	0.00% <0.00%> (ø)
panel/tests/ui/widgets/test_tabulator.py	99.06% <0.00%> (+0.10%)	⬆️
panel/pane/idom.py	28.36% <0.00%> (+0.19%)	⬆️
panel/tests/conftest.py	88.79% <0.00%> (+0.38%)	⬆️
panel/io/callbacks.py	79.85% <0.00%> (+0.59%)	⬆️
... and 1 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[MarcSkovMadsen]

I think I see the speedups from the new CDN in Panel 0.14. It seems more snappy.

I noticed pyodide is coming from jsdelivr. If you ever talk to those guys they might consider running their own cdn one day.