Fix T4 Serial3 CTS pin.

Had wrong pin in my table, so fixed table.

User found on forum: https://forum.pjrc.com/threads/58414-Teensy-4-0-Serial3-attachCts-wrong-pin-in-HardwareSerial3-cpp?p=221464#post221464

teensy4/HardwareSerial3.cpp

 	CCM_CCGR0, CCM_CCGR0_LPUART2(CCM_CCGR_ON),
 	{{15,2, &IOMUXC_LPUART2_RX_SELECT_INPUT, 1}, {0xff, 0xff, nullptr, 0}},
 	{{14,2, nullptr, 0}, {0xff, 0xff, nullptr, 0}},
-	18, //IOMUXC_SW_MUX_CTL_PAD_GPIO_AD_B1_01, // 18
+	19, //IOMUXC_SW_MUX_CTL_PAD_GPIO_AD_B1_00, // 19
 	2, // page 473 
 	IRQ_PRIORITY, 38, 24, // IRQ, rts_low_watermark, rts_high_watermark
 };