Merge bitcoin/bitcoin#28194: test: python E721 and flake8 updates

bee2d57a65 script: update flake8 to 6.1.0 (Jon Atack)
38c3fd846b test: python E721 updates (Jon Atack)

Pull request description:

  Update our functional tests per [E721](https://www.flake8rules.com/rules/E721.html) enforced by [flake8 6.1.0](https://flake8.pycqa.org/en/latest/release-notes/6.1.0.html), and update our CI lint task to use that release.  This makes the following linter output on current master with flake8 6.1.0 green.

  ```
  $ ./test/lint/lint-python.py ; ./test/lint/lint-spelling.py
  test/functional/p2p_invalid_locator.py:35:16: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
  test/functional/test_framework/siphash.py:34:12: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
  test/functional/test_framework/siphash.py:64:12: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
  src/test/fuzz/descriptor_parse.cpp:88: occurences ==> occurrences
  ^ Warning: codespell identified likely spelling errors. Any false positives? Add them to the list of ignored words in test/lint/spelling.ignore-words.txt
  ```

ACKs for top commit:
  MarcoFalke:
    lgtm ACK bee2d57a65

Tree-SHA512: f3788a543ca98e44eeeba1d06c32f1b11eec95d4aef068aa1b6b5c401261adfa3fb6c6d6c769f3fe6839d78e74a310d5c926867e7c367d6513a53d580fd376f3

test/functional/test_framework/siphash.py

@@ -31,7 +31,7 @@ def siphash_round(v0, v1, v2, v3):
 
 
 def siphash(k0, k1, data):
-    assert type(data) == bytes
+    assert type(data) is bytes
     v0 = 0x736f6d6570736575 ^ k0
     v1 = 0x646f72616e646f6d ^ k1
     v2 = 0x6c7967656e657261 ^ k0
@@ -61,5 +61,5 @@ def siphash(k0, k1, data):
 
 
 def siphash256(k0, k1, num):
-    assert type(num) == int
+    assert type(num) is int
     return siphash(k0, k1, num.to_bytes(32, 'little'))