Cirrus: Mark E722 linter as mandatory (#8668)

These linter warnings were all fixed in
312f2641e7, so making CI enforce them will
reduce the risk of regressions.

Co-authored-by: Jeremy Rand <jeremyrand@danwin1210.de>

.cirrus.yml

@@ -141,7 +141,7 @@ task:
         # - https://flake8.pycqa.org/en/latest/user/error-codes.html
         # - https://pycodestyle.pycqa.org/en/latest/intro.html#error-codes
         # - 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: E9,E101,E129,E273,E274,E703,E71,E722,F63,F7,F82,W191,W29,B
         ELECTRUM_LINTERS_IGNORE: B007,B009,B010,B019
     - name: "linter: Flake8 Non-Mandatory"
       env: