package/python-magic-wormhole-mailbox-server: add missing reverse dependency on host-rustc

As reported by Yann in [1], Kconfig warns about an unmet dependency.

The issue can be reproduced on master branch at commit 451672e,
with the command:

    KCONFIG_SEED=0x1D15B9D4 make randconfig

The patch adds the missing dependency.

Fixes:

    WARNING: unmet direct dependencies detected for BR2_PACKAGE_PYTHON_AUTOBAHN
      Depends on [n]: BR2_PACKAGE_PYTHON3 [=y] && BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS [=n]
      Selected by [y]:
      - BR2_PACKAGE_PYTHON_MAGIC_WORMHOLE_MAILBOX_SERVER [=y] && BR2_PACKAGE_PYTHON3 [=y]

[1] https://lists.buildroot.org/pipermail/buildroot/2023-February/661898.html

Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/python-magic-wormhole-mailbox-server/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_PYTHON_MAGIC_WORMHOLE_MAILBOX_SERVER
 	bool "python-magic-wormhole-mailbox-server"
+	depends on BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS # python-autobahn -> python-cryptography
 	select BR2_PACKAGE_PYTHON3_SQLITE # runtime
 	select BR2_PACKAGE_PYTHON_ATTRS # runtime
 	select BR2_PACKAGE_PYTHON_AUTOBAHN # runtime