Fix docstring of Index.join in base.py
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That's a very strange thing and it's better if pandas devs can have a closer look here.

I can see the `Examples` have been added with https://github.com/pandas-dev/pandas/pull/53403 but there is no sign of any failure. Everything looks good over there (cc @DeaMariaLeon @MarcoGorelli).

 > Everything looks good over there (

I did not look far down enough. The "Examples" heading is indeed one space to far to the right. So this PR should fix it. Nice thanks @kmuehlbauer  @mroeschke @lithomas1 Could this be included into 2.1.1? This breaks doc-building downstream. @meeseeksdev backport 2.1.x