v2.20.0

This is a major Buildroot, toolchain, and Linux kernel update.

Please see nerves_system_br v1.25.0 release notes
for upgrade instructions if you've forked this system.

The Linux kernel update from 5.10 to 6.1 has a side effect of renumbering GPIOs.
Circuits.GPIO v1.2 accounts for this so programs don't need to change that use
it. See elixir-circuits/circuits_gpio#153 for more
information. This system has an optional dependency on Circuits.GPIO to force
the upgrade.

• Updated dependencies
  • Linux 6.1.46-ti-r13
  • nerves_system_br v1.25.2
  • Buildroot 2023.08.4
  • Erlang/OTP 26.1.2