build.yml: Adjust for change in 'brew'
build.yml: Adjust for change in 'brew'

'brew' apparently introduced an incompatible change, where even
"--force" does not actually make the commands available in the default path.

Also switch to a numbered macos release instead of "latest", though this
did not save us from breaking changes in brew or other preinstalled sw.

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/micropython,adafruit/micropython