sphinx conf warning fix

[speediedan]

Before submitting

Closes #178

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Fixes #174
Explicitly reference language = "en" to avoid new warning.

Note build-docs check will not pass until #176 is merged. CI testing/nbval check won't pass until #178 is merged.

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

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[codecov]

Codecov Report

Merging #175 (36aef23) into main (3fda6eb) will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff         @@
##           main   #175   +/-   ##
===================================
  Coverage    75%    75%           
===================================
  Files         2      2           
  Lines       370    370           
===================================
  Hits        276    276           
  Misses       94     94           

[Borda]

seem that there is a dead-lock with #178 as that one can't pass CI for missing lang, and this can not build for broken ffmpeg