Updated adafruit_si4713.py to also recognize the si4721 chip.

It will work in analog input mode as the si4713 chip.
Digital input not yet tested, will be done later

Author: sheimers

README.rst

@@ -13,7 +13,7 @@ Introduction
     :target: https://github.com/adafruit/Adafruit_CircuitPython_SI4713/actions/
     :alt: Build Status
 
-CircuitPython module for SI4713 FM RDS transmitter.
+CircuitPython module for SI4713 and SI4721 FM RDS transmitter.
 
 Dependencies
 =============

adafruit_si4713.py

@@ -122,8 +122,8 @@ def __init__(self, i2c, *, address=_SI4710_ADDR1, reset=None, timeout_s=0.1):
         self._device = i2c_device.I2CDevice(i2c, address)
         self.reset()
         # Check product ID.
-        if self._get_product_number() != 13:
-            raise RuntimeError("Failed to find SI4713, check wiring!")
+        if self._get_product_number() != 13 and self._get_product_number() != 21:
+            raise RuntimeError("Failed to find SI4713 or SI4721, check wiring!")
 
     def _read_u8(self, address):
         # Read an 8-bit unsigned value from the specified 8-bit address.