fix: remove real WiFi credentials from ThinkNode M5 variant

variants/thinknode_m5/platformio.ini contained actual WiFi SSID and
password credentials (Livebox-633C) committed by mistake. Replaced
with placeholder values consistent with other variants (myssid/mypwd).

variants/thinknode_m5/platformio.ini

@@ -193,8 +193,8 @@ build_flags =
   -D MAX_GROUP_CHANNELS=40
   -D OFFLINE_QUEUE_SIZE=256
   -D WIFI_DEBUG_LOGGING=1
-  -D WIFI_SSID='"Livebox-633C"'
-  -D WIFI_PWD='"vvQUHGSxsWd7fKMYSr"'
+  -D WIFI_SSID='"myssid"'
+  -D WIFI_PWD='"mypwd"'
 build_src_filter = ${ThinkNode_M5.build_src_filter}
   +<helpers/esp32/*.cpp>
   +<helpers/ui/MomentaryButton.cpp>