Meta: Don't pass ^C through the serial console on CI

`-serial mon:stdio` passes through all kinds of key combinations,
`-serial stdio` doesn't. This probably isn't something that we want
while running tests or CI, so switch to the non-passing variant.

aarch64 actually failed to run due to this, since it already had
`-serial stdio` in its arguments, causing a conflict. This is why that
entry is now gone entirely.

Meta/run.sh

@@ -523,7 +523,6 @@ elif [ "$SERENITY_RUN" = "ci" ]; then
             -M raspi3b \
             -d guest_errors \
             -no-reboot \
-            -serial mon:stdio \
             -monitor none \
             -display none \
             -serial file:debug.log \
@@ -541,7 +540,7 @@ elif [ "$SERENITY_RUN" = "ci" ]; then
             -no-reboot \
             -smp ${SERENITY_CPUS} \
             -device ich9-ahci \
-            -serial mon:stdio \
+            -serial stdio \
             -display none \
             -debugcon file:debug.log \
             $SERENITY_KERNEL_AND_INITRD \