Pymor

This is a bugfix-only release. Since the release of 2022.2.0 version 8 of ipywidgets was released, which is incompatible with our current Jupyter notebook visualizations. As a stop-gap measure we've pinned `ipywidgets<8` [in our packaging](https://github.com/pymor/pymor/pull/1724).
Additionally this bugfix release removes spurious import warnings in our [documentation and tutorials](https://github.com/pymor/pymor/pull/1710).

HenKlei, peoe, artpelling and ullmannsven.
See [here](https://github.com/pymor/pymor/blob/main/AUTHORS.md) for more details.

This is a bugfix release. The only change compared to 2021.2.0 is preventing users to face https://github.com/pymor/pymor/issues/1533 due to an upstream bug in [qtpy](https://github.com/spyder-ide/qtpy/)

The full release notes for 2021.2 can be found [here](https://docs.pymor.org/2021-2-1/release_notes/all.html#pymor-2021-2-december-22-2021).

Henrike von Hülsen. See [here](https://github.com/pymor/pymor/blob/main/AUTHORS.md)
for more details.