Fix synapse filt to allow list as input

[arvoelke]

Description:
Fixes a bug where Synapse.filt could not accept a list as input.

Motivation and context:
Lowpass(0.005).filt([1, 0, 0]) would raise the error AttributeError: 'list' object has no attribute 'dtype'. There is no issue for this bug.

How has this been tested?
Changed a test from u -> list(u).

Where should a reviewer start?
One line in synapses.py.

How long should this take to review?

• Quick (less than 40 lines changed or changes are straightforward)

Types of changes:

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have read the CONTRIBUTING.rst document.
• I have updated the documentation accordingly.
• I have included a changelog entry.
• I have added tests to cover my changes.
• All new and existing tests passed.

[mention-bot]

@arvoelke, thanks for your PR! By analyzing the annotation information on this pull request, we identified @tbekolay to be a potential reviewer

[arvoelke]

Let me know if it's worthwhile to add a test and then I can, but in general it seems silly to test lists on array_like interfaces unless there's something critical going on. Also didn't think this was worthy of bloating the changelog.

[tbekolay]

I'd say rather than adding a test, modify an existing tests to use a list (just call tolist or something). Why don't you think this is changelog worthy?

[arvoelke]

Done both.

[hunse]

LGTM

[jgosmann]

LGTM 🍰

[tbekolay]

LGTM too, I'll merge 👍