Ensure load_notebook is executed only once

[philippjfr]

No description provided.

[codecov]

Codecov Report

Merging #1000 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1000      +/-   ##
==========================================
- Coverage   85.86%   85.84%   -0.02%     
==========================================
  Files          99       99              
  Lines       11305    11307       +2     
==========================================
  Hits         9707     9707              
- Misses       1598     1600       +2

Impacted Files	Coverage Δ
panel/config.py	52.43% <0%> (-0.65%)	⬇️

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