logging: fix color for shell log backend

This allows CONFIG_LOG_BACKEND_SHOW_COLOR to be configured when logging
to shell.

Signed-off-by: Xudong Zheng <7pkvm5aw@slicealias.com>

Author: xudongzheng

subsys/logging/Kconfig.formatting

@@ -135,7 +135,7 @@ config LOG_IMMEDIATE_CLEAN_OUTPUT
 config LOG_BACKEND_SHOW_COLOR
 	bool "Colors in the backend"
 	depends on LOG_BACKEND_UART || LOG_BACKEND_NATIVE_POSIX || LOG_BACKEND_RTT \
-	           || LOG_BACKEND_SWO || LOG_BACKEND_XTENSA_SIM
+	           || LOG_BACKEND_SWO || LOG_BACKEND_XTENSA_SIM || SHELL_LOG_BACKEND
 	default y
 	help
 	  When enabled selected backend prints errors in red and warning in yellow.