doc: release_cycle: fix next release version

The release commit for version v2025.04 forgot to update the next
version (i. e. v2025.07) in the section where information about the
merge window is provided.

Fixes: 34820924edbc ("Prepare v2025.04")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
1 file changed