Fix "== None" linter fails

Credit to Zoltan Konder for pointing me to this issue.

electrum/plugins/bitbox02/bitbox02.py

@@ -444,7 +444,7 @@ class BitBox02Client(HardwareClientBase):
                 }
             )
 
-            if tx_script_type == None:
+            if tx_script_type is None:
                 tx_script_type = txin.script_type
             elif tx_script_type != txin.script_type:
                 raise Exception("Cannot mix different input script types")

electrum/plugins/coldcard/coldcard.py

@@ -228,7 +228,7 @@ class CKCCClient(HardwareClientBase):
         resp = self.dev.send_recv(CCProtocolPacker.sign_transaction(dlen, chk, finalize=finalize),
                                     timeout=None)
 
-        if resp != None:
+        if resp is not None:
             raise ValueError(resp)
 
     @runs_in_hwd_thread

electrum/rsakey.py

@@ -79,7 +79,7 @@ def numberToByteArray(n, howManyBytes=None):
     not be larger.  The returned bytearray will contain a big-endian
     encoding of the input integer (n).
     """
-    if howManyBytes == None:
+    if howManyBytes is None:
         howManyBytes = numBytes(n)
     b = bytearray(howManyBytes)
     for count in range(howManyBytes-1, -1, -1):

electrum/tests/test_bolt11.py

@@ -49,7 +49,7 @@ class TestBolt11(ElectrumTestCase):
         b.tags = [t for t in b.tags if t[0] != 'h' and t[0] != 'n']
 
         assert b.pubkey.serialize() == PUBKEY, (hexlify(b.pubkey.serialize()), hexlify(PUBKEY))
-        assert b.signature != None
+        assert b.signature is not None
 
         # Unset these, they are generated during encoding/decoding
         b.pubkey = None