[Python] Fix Cert API argument type errors

NativeLibraryHandleMethodArguments correctly setting the argument
types causes argument type errors:
ctypes.ArgumentError: argument 1: TypeError: expected LP_c_ubyte instance instead of bytes

We can safely cast bytes as the native side marks it const.

src/controller/python/chip/credentials/cert.py

@@ -35,8 +35,10 @@ def convert_x509_cert_to_chip_cert(x509Cert: bytes) -> bytes:
     """Converts a x509 certificate to CHIP Certificate."""
     output_buffer = (ctypes.c_uint8 * 1024)()
     output_size = ctypes.c_size_t(1024)
+    ptr_type = ctypes.POINTER(ctypes.c_uint8)
 
-    _handle().pychip_ConvertX509CertToChipCert(x509Cert, len(x509Cert), output_buffer, ctypes.byref(output_size)).raise_on_error()
+    _handle().pychip_ConvertX509CertToChipCert(ctypes.cast(x509Cert, ptr_type), len(x509Cert),
+                                               ctypes.cast(output_buffer, ptr_type), ctypes.byref(output_size)).raise_on_error()
 
     return bytes(output_buffer)[:output_size.value]
 
@@ -45,7 +47,9 @@ def convert_chip_cert_to_x509_cert(chipCert: bytes) -> bytes:
     """Converts a x509 certificate to CHIP Certificate."""
     output_buffer = (ctypes.c_byte * 1024)()
     output_size = ctypes.c_size_t(1024)
+    ptr_type = ctypes.POINTER(ctypes.c_uint8)
 
-    _handle().pychip_ConvertChipCertToX509Cert(chipCert, len(chipCert), output_buffer, ctypes.byref(output_size)).raise_on_error()
+    _handle().pychip_ConvertChipCertToX509Cert(ctypes.cast(chipCert, ptr_type), len(chipCert),
+                                               ctypes.cast(output_buffer, ptr_type), ctypes.byref(output_size)).raise_on_error()
 
     return bytes(output_buffer)[:output_size.value]