CI is failing on `main` due to flake8

[nealrichardson]

See https://github.com/posit-dev/py-shiny/actions/runs/7538643088/job/20519572273 for example

flake8 --show-source .
./shiny/_utils.py:396:13: B036 Don't except `BaseException` unless you plan to re-raise it.
            except BaseException as e:
            ^
./shiny/_utils.py:422:9: B036 Don't except `BaseException` unless you plan to re-raise it.
        except BaseException as e:
        ^
./shiny/render/renderer/_renderer.py:228:13: B037 Class `__init__` methods must not return or yield and any values.
            return cast(AsyncValueFn[IT], fn)
            ^