On Ubuntu 20.10, we build against ModemManager 1.14.0 and get a compiler warning:

  ../src/devices/wwan/nm-modem-broadband.c: In function 'try_create_connect_properties':
  ../src/devices/wwan/nm-modem-broadband.c:492:2: error: 'MMModemCapabilityDeprecated' is deprecated [-Werror=deprecated-declarations]
    492 |  if (MODEM_CAPS_3GPP (ctx->caps)) {
        |  ^~

Suppress it.

An alternative would be to drop the flag entirely. It seems the flag
was never used (and never will be used). But if that's true, there is
little harm done checking it. If it's not true, we better keep checking
for older versions.

mobile-broadband/ModemManager@0cd76bf1