uboot-test-hooks: Switch to our GitLab instance

As Stephen is no longer actively maintaining the uboot-test-hooks
repository, switch to using the instance on our GitLab.

Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/doc/develop/py_testing.rst b/doc/develop/py_testing.rst
index f71e837..7f01858 100644
--- a/doc/develop/py_testing.rst
+++ b/doc/develop/py_testing.rst
@@ -301,7 +301,7 @@
 Examples
 ''''''''
 
-https://github.com/swarren/uboot-test-hooks contains some working example hook
+https://source.denx.de/u-boot/u-boot-test-hooks contains some working example hook
 scripts, and may be useful as a reference when implementing hook scripts for
 your platform. These scripts are not considered part of U-Boot itself.