add kiss radio env to most of the variants

variants/xiao_rp2040/platformio.ini

@@ -108,3 +108,8 @@ build_src_filter = ${Xiao_rp2040.build_src_filter}
   +<../examples/simple_secure_chat/main.cpp>
 lib_deps = ${Xiao_rp2040.lib_deps}
   densaugeo/base64 @ ~1.4.0
+
+[env:Xiao_rp2040_kiss_modem]
+extends = Xiao_rp2040
+build_src_filter = ${Xiao_rp2040.build_src_filter}
+  +<../examples/kiss_modem/>