Add Arduino Giga support / Fix Arduino giga_r1_m7 build error

[NotLe0n]

This small change fixes a linker error when building on the Arduino Giga board. Since everthing seems to function correctly I added it to the supported boards table. Feel free to remove the entry if it turns out to not be.

This was the error it fixes:

... lots of other random symbols ...
.pio/libdeps/serial/micro_ros_platformio/libmicroros/libmicroros.a(libtest_msgs__rosidl_typesupport_microxrcedds_c__unbounded_sequences__type_support_c.c.obj): In function `_UnboundedSequences__cdr_deserialize':
unbounded_sequences__type_support_c.c:(.text._UnboundedSequences__cdr_deserialize+0x1f2): undefined reference to `rosidl_typesupport_microxrcedds_c__get_message_type_support_handle__test_msgs__msg__BasicTypes'
.pio/libdeps/serial/micro_ros_platformio/libmicroros/libmicroros.a(libtest_msgs__rosidl_typesupport_microxrcedds_c__unbounded_sequences__type_support_c.c.obj): In function `_UnboundedSequences__cdr_serialize':
unbounded_sequences__type_support_c.c:(.text._UnboundedSequences__cdr_serialize+0x110): undefined reference to `rosidl_typesupport_microxrcedds_c__get_message_type_support_handle__test_msgs__msg__BasicTypes'
collect2: error: ld returned 1 exit status
*** [.pio/build/serial/firmware.elf] Error 1