Bump mini-gdbstub to latest version

RinHizakura · RinHizakura · commit 855b4289fcda · 2025-09-07T16:19:50.000+08:00
The commit 78b00cd of mini-gdbstub avoids busy
waiting, which prevents CPU utilization from
going to 100%.
diff --git a/mini-gdbstub b/mini-gdbstub
@@ -1 +1 @@
-Subproject commit 18a3746fda1a03d82b31bc6b8f15c47e5808cee1
+Subproject commit 78b00cdfb1352ca80117832a898919d58d47b53b
