[openthread] Disable default enabled OT diag code (#14399)

esphome/components/openthread/__init__.py

@@ -53,6 +53,9 @@ def set_sdkconfig_options(config):
     # There is a conflict if the logger's uart also uses the default UART, which is seen as a watchdog failure on "ot_cli"
     add_idf_sdkconfig_option("CONFIG_OPENTHREAD_CLI", False)
 
+    # Diag unused, if needed for lab/cert/etc tests then enable separately
+    add_idf_sdkconfig_option("CONFIG_OPENTHREAD_DIAG", False)
+
     add_idf_sdkconfig_option("CONFIG_OPENTHREAD_ENABLED", True)
 
     if tlv := config.get(CONF_TLV):