Crash when changing the language of .ipynb files

https://sentry.softwareheritage.org/organizations/swh/issues/105499/?referrer=phabricator_plugin

ReferenceError: updateLanguage is not defined
  at HTMLSelectElement.<anonymous> (/browse/content/sha1_git:d028b549147fa4e141085ab0f1632b4bd59d9570/:57:7)
...
(10 additional frame(s) were not displayed)

To reproduce:

1. go to https://archive.softwareheritage.org/browse/content/sha1_git:952fa1244ac341e455227c3a6b204a5dd93aeb26/?path=b0e6b36cf0c771d3a075f4be74621e034391f6fd/1-1-0_Presentation.ipynb
2. click any language in the language picker

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Migrated from T4725 (view on Phabricator)