Update .gitattributes - mark *.recipe as linguist-language=python

Sometimes syntax highlighting is picked up correctly on GitHub which uses linguist[^1], when the `*.recipe` includes a shebang for python it will syntax highlight. Other times it does not.

This change adds an attribute to `*.recipe` to mark it as a python language to linguist, following the documentation on overrides[^2].

Example without highlighting: [recipes/ad.recipe]

Example with highlighting (python syntax picked up via shebang):
[recipes/ambito_financiero.recipe]


[^1]: https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-repository-languages
[^2]: https://github.com/github-linguist/linguist/blob/559a6426942abcae16b6d6b328147476432bf6cb/docs/overrides.md


[recipes/ad.recipe]: https://github.com/kovidgoyal/calibre/blob/aeb19dfedfe14c5ee8d454c831d634e81219bf44/recipes/ad.recipe
[recipes/ambito_financiero.recipe]: https://github.com/kovidgoyal/calibre/blob/aeb19dfedfe14c5ee8d454c831d634e81219bf44/recipes/ambito_financiero.recipe

.gitattributes

@@ -1,7 +1,7 @@
 # Tell git what files are txt
 *.py  text diff=python
 *.pyj  text diff=python
-*.recipe  text diff=python
+*.recipe  text diff=python linguist-language=python
 *.coffee  text
 *.js      text
 *.pot     text