Fix mutating the application registry

[keewis]

When adding the ApplicationRegistry class I apparently forgot to forward __setattr__. This means that trying to mutate the application registry does not change the wrapped registry, but rather adds a new attribute to ApplicationRegistry:

from pint import application_registry as ureg

ureg.force_ndarray_like = True
assert ureg.force_ndarray_like is True
assert ureg._registry.force_ndarray_like is True  # AssertionError

Since this is included in v0.18, we might need a new release soon. What do you think, @hgrecco, @jules-ch

• Executed pre-commit run --all-files with no errors
• The change is fully covered by automated unit tests
• Added an entry to the CHANGES file

[keewis]

I'm not sure if that was a random failure on RTD, but pinning sphinx>4 seems to have worked

[jules-ch]

I've explained the error in RTD build here #1399 (comment).
We need to get rid of those hard coded dependencies. We can pin sphinx version like you did in the meantime

Looks good to me.
We can do a 0.18.1 release

[keewis]

great. Should I add a note to CHANGES?

[keewis]

oh, and is it fine to keep the pin in this PR?

[jules-ch]

Yes Add this fix in CHANGES & keep the pin I'll pin other docs dependencies in another PR.

[keewis]

add this fix in CHANGES

done

[jules-ch]

Thanks @keewis