tests: driver: build-test: add min_ram restriction

below two build test can not fit in SRAM size

drivers.modem.build
drivers.modem.quectel_bg9x.build

build error report:

region `SRAM' overflowed by 20688 bytes
collect2: error: ld returned 1 exit status

Signed-off-by: Hake Huang <hake.huang@oss.nxp.com>