Update another tranche of REP links. (#6022) (#6036)

(cherry picked from commit 33ebc2f)

Signed-off-by: Alejandro Hernández Cordero <[email protected]>
Co-authored-by: Katherine Scott <[email protected]>
Co-authored-by: Alejandro Hernández Cordero <[email protected]>

Author: 3 people

source/How-To-Guides/Using-Variants.rst

@@ -15,7 +15,7 @@ In addition to the official variants, there may be metapackages for specific ins
 Adding variants
 ---------------
 
-Additional variants that are of general use to the ROS community can be proposed by contributing an update to `REP-2001 via pull request <https://github.com/ros-infrastructure/rep/blob/master/rep-2001.rst>`_ describing the packages included in the new variant.
+Additional variants that are of general use to the ROS community can be proposed by contributing an update to `REP-2001 via pull request <https://github.com/openrobotics/reps/blob/main/_posts/rep-2001.md>`_ describing the packages included in the new variant.
 Institution and robot specific variants can be published directly by their respective maintainers and no update to REP-2001 is required.
 
 Creating project-specific variants