docs: apply some redirects

Here's a few redirects that we should apply, in case the redirects
gets removed in the future.

These are mostly of the 301 (moved permanently) kind, but also a
few where the site probably *should* have used the permanent
error-code.

Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19574>

docs/relnotes/20.0.0.rst

@@ -156,7 +156,7 @@ Bug fixes
 -  [Bisected] i965: CS:GO crashes in emit_deref_copy_load_store with
    debug Mesa
 -  radv/aco Jedi Fallen Order hair rendering buggy
--  Inaccurate information on https://www.mesa3d.org/repository.html
+-  Inaccurate information on https://docs.mesa3d.org/repository.html
    about how to get git write access.
 -  [RADV] VK_KHR_timeline_semaphore balloons in runtime
 -  Shadow of Mordor has randomly dancing black shadows on Talion's face

docs/relnotes/6.5.2.rst

@@ -43,7 +43,7 @@ New features
 -  New ``minstall`` script to replace normal install program
 -  Faster fragment program execution in software
 -  Added (or fixed) support for
-   `GLX_SGI_make_current_read <https://www.khronos.org/registry/OpenGL/extensions/SGI/GLX_SGI_make_current_read.txt>`__
+   `GLX_SGI_make_current_read <https://registry.khronos.org/OpenGL/extensions/SGI/GLX_SGI_make_current_read.txt>`__
    to the following drivers:
 
    -  radeon