[AIRFLOW-6528] disable flake8 W503 line break before binary operator

[dstandish]

Flake8's W503 rule says there should be no line break before binary operator.

This rule is incompatible with black formatter, and is also in my opinion less readable.

Status quo example with W503 check enabled:

    @property
    def sqlalchemy_scheme(self):
        return (
            self._sqlalchemy_scheme or
            self.connection_extra_lower.get('sqlalchemy_scheme') or
            self.DEFAULT_SQLALCHEMY_SCHEME
        )

as required by black (W503 disabled)

    @property
    def sqlalchemy_scheme(self):
        return (
            self._sqlalchemy_scheme
            or self.connection_extra_lower.get('sqlalchemy_scheme')
            or self.DEFAULT_SQLALCHEMY_SCHEME
        )

---

Issue link: AIRFLOW-6528

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---

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[potiuk]

@mik-laj - what do you think - I am ok with it :)

[potiuk]

Thanks @dstandish !