JOSS Paper: Reduce line-spacing in code blocks

[Andrew-S-Rosen]

Summary

The code-blocks have two line breaks in many places, in accordance with black. However, the generous line-spacing is somewhat bothersome in a journal article format. I had intended there to be only one line break, but I think Alex's text editor may have auto-reformatted it upon upload. This PR reverts back to the single line-break format I had intended.

Partially addresses (but does not close) #453.

@janosh: Could you please merge this too? Thanks!

Edit: How can we have the lint test skip the paper.md file altogether?

[codecov[bot]]

Codecov Report

Merging #454 (d178f63) into main (cdbcbd0) will not change coverage. Report is 2 commits behind head on main. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #454 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 20 20 Lines 1521 1521 Branches 419 419 ========================================= Hits 1521 1521 ```