Merge RIOT-OS#19979

19979: dist/testbed-support: Add openmote board r=aabadie a=MrKevinWeiss

### Contribution description

As part of fixing the automated release specs test we will need support for another `cc2538` based board.  I was able to get the tests passing with adaption here and to the release specs.

### Testing procedure

### Issues/PRs references


Co-authored-by: MrKevinWeiss <weiss.kevin604@gmail.com>

dist/testbed-support/makefile.iotlab.archi.inc.mk

@@ -10,6 +10,7 @@ IOTLAB_ARCHI_microbit       = microbit:ble
 IOTLAB_ARCHI_nrf52dk        = nrf52dk:ble
 IOTLAB_ARCHI_nrf52840dk     = nrf52840dk:multi
 IOTLAB_ARCHI_nucleo-wl55jc  = nucleo-wl55jc:stm32wl
+IOTLAB_ARCHI_openmote-b     = openmoteb
 IOTLAB_ARCHI_samr21-xpro    = samr21:at86rf233
 IOTLAB_ARCHI_samr30-xpro    = samr30:at86rf212b
 IOTLAB_ARCHI_samr34-xpro    = samr34:sx1276