channels.cfg: stable(-next) -> v20.05/v21.03

Prepare for the upcoming release based on Alpine 3.14.

Closes: https://gitlab.com/postmarketOS/pmbootstrap/-/issues/2015

channels.cfg

@@ -8,17 +8,13 @@ branch_pmaports=master
 branch_aports=master
 mirrordir_alpine=edge
 
-# NOTE: "stable", "stable-next" are actually "v20.05" and "v21.03". They will
-# get changed in this file in the near future, keeping the old names for a bit
-# to give everybody time to upgrade to pmbootstrap 1.30.0. More information:
-# https://gitlab.com/postmarketOS/pmbootstrap/-/issues/2015
-[stable-next]
+[v21.03]
 description=Latest release / Recommended for best stability
 branch_pmaports=v21.03
 branch_aports=3.13-stable
 mirrordir_alpine=v3.13
 
-[stable]
+[v20.05]
 description=Old release (unsupported)
 branch_pmaports=v20.05
 branch_aports=3.12-stable