Since release 2022.2.14 the "show source" button does not appear

[pvergain]

Hello and thank you for the furo theme !

Since the 2022.2.14 release the "show source" button does not appear.

Reproduction

• clone the https://github.com/Mariatta/sphinx-intro-tutorial.git
• Install the last furo release (2022.4.7)
• produce the documentation

We can see that there is no "Show button"

• install the 2022.1.2 furo version
• produce the documentation

And now we have the "Show source button"

So I use the 2022.1.2 release.

[pradyunsg]

See #374