Fix filename error.

Author: is-qian

boards.txt

@@ -34947,7 +34947,7 @@ XIAO_ESP32S3_PLUS.build.bootloader_addr=0x0
 XIAO_ESP32S3_PLUS.build.target=esp32s3
 XIAO_ESP32S3_PLUS.build.mcu=esp32s3
 XIAO_ESP32S3_PLUS.build.core=esp32
-XIAO_ESP32S3_PLUS.build.variant=XIAO_ESP32S3_PLUS
+XIAO_ESP32S3_PLUS.build.variant=XIAO_ESP32S3_Plus
 XIAO_ESP32S3_PLUS.build.board=XIAO_ESP32S3_PLUS
 
 XIAO_ESP32S3_PLUS.build.usb_mode=0