Fixed incorrect board name for TinyPICO - You can now use this to det…

…ect it's a TinyPICO at compile time.... (#3567)

#ifdef ARDUINO_TINYPICO
   // It's a TinyPICO!
#endif

boards.txt

@@ -324,7 +324,7 @@ tinypico.serial.disableRTS=true
 tinypico.build.mcu=esp32
 tinypico.build.core=esp32
 tinypico.build.variant=pico32
-tinypico.build.board=ESP32_PICO
+tinypico.build.board=TINYPICO
 
 tinypico.build.f_cpu=240000000L
 tinypico.build.flash_size=4MB