Fixed typo in developer-setup

Summary:
(T1696)
Fixed a typo in developer-setup. In the second line of the first point, it should be your modifications instead of yout modifications.

Reviewers: #reviewers, zack

Reviewed By: #reviewers, zack

Differential Revision: https://forge.softwareheritage.org/D1437

docs/developer-setup.rst

@@ -78,7 +78,7 @@ Unit tests are using the pytest_ framework, and can be executed directly or via
 tox_. The main difference between these 2 test execution environments is:
 
 - When executed via tox_, all the dependencies (including swh ones) are
-  installed from pypi_: you test yout modifications against the latest
+  installed from pypi_: you test your modifications against the latest
   published version of every swh package but the current one.
 
 - When you execute pytest_ directly, swh dependencies are used from your