build: hotfix for Schism clockrate issue

Reduced CPU frequency for Schism config down to 130MHz as it seems it
was for some unknown reason interfering with i2c comms resulting in the
right hand side not working. Will need to do some debugging of this in
future.

Author: JonnyHaystack

config/schism/env.ini

@@ -1,5 +1,6 @@
 [env:schism]
 extends = arduino_pico_base
+board_build.f_cpu = 130000000L
 build_src_filter =
     ${arduino_pico_base.build_src_filter}
     +<config/schism>