Fixing a few test things

[tlambert03]

• unregisters the types from the new waveform example
• closes widgets after each test

[codecov]

Codecov Report

Merging #325 (abe233c) into main (28643f2) will decrease coverage by 0.10%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #325      +/-   ##
==========================================
- Coverage   90.30%   90.19%   -0.11%     
==========================================
  Files          29       29              
  Lines        3302     3357      +55     
==========================================
+ Hits         2982     3028      +46     
- Misses        320      329       +9     

Impacted Files	Coverage Δ
magicgui/widgets/_function_gui.py	94.44% <0.00%> (-3.33%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 28643f2...abe233c. Read the comment docs.