CI: also run flake8-bugbear, as part of flake8

.cirrus.yml

@@ -132,9 +132,9 @@ task:
     folder: ~/.cache/pip
     fingerprint_script: echo Flake8 && echo $ELECTRUM_IMAGE && cat $ELECTRUM_REQUIREMENTS
   install_script:
-    - pip install flake8
+    - pip install flake8 flake8-bugbear
   flake8_script:
-    - flake8 . --count --select=$ELECTRUM_LINTERS --show-source --statistics --exclude "*_pb2.py"
+    - flake8 . --count --select="$ELECTRUM_LINTERS" --ignore="$ELECTRUM_LINTERS_IGNORE" --show-source --statistics --exclude "*_pb2.py,electrum/_vendor/"
   env:
     ELECTRUM_IMAGE: python:3.8
     ELECTRUM_REQUIREMENTS: contrib/requirements/requirements.txt
@@ -144,10 +144,13 @@ task:
         # list of error codes:
         # - https://flake8.pycqa.org/en/latest/user/error-codes.html
         # - https://pycodestyle.pycqa.org/en/latest/intro.html#error-codes
-        ELECTRUM_LINTERS: E9,E101,E129,E273,E274,E703,E71,F63,F7,F82,W191,W29
+        # - https://github.com/PyCQA/flake8-bugbear/tree/8c0e7eb04217494d48d0ab093bf5b31db0921989#list-of-warnings
+        ELECTRUM_LINTERS: E9,E101,E129,E273,E274,E703,E71,F63,F7,F82,W191,W29,B
+        ELECTRUM_LINTERS_IGNORE: B007,B009,B010,B019
     - name: Flake8 Non-Mandatory
       env:
-        ELECTRUM_LINTERS: E,F,W,C90
+        ELECTRUM_LINTERS: E,F,W,C90,B
+        ELECTRUM_LINTERS_IGNORE: ""
       allow_failures: true
 
 task: