examples/rust-gcoap: Update Makefile.ci

Some increase in binary size is expected due to one bug fix around the
VFS access where a zero-cost version would require threading
non-idiomatic nul-terminated strings through too many abstraction levels
to be practical.

examples/rust-gcoap/Makefile.ci

@@ -17,6 +17,7 @@ BOARD_INSUFFICIENT_MEMORY := \
     hifive1b \
     i-nucleo-lrwan1 \
     im880b \
+    lobaro-lorabox \
     lsn50 \
     maple-mini \
     microbit \