TEST: Finalize deprecations

[effigies]

Forgot to test before release that DeprecationWarnings were promoted to ExpiredDeprecationErrors. Will fix this and release 4.0.1.

[codecov]

Codecov Report

Merging #1117 (d1b66c5) into maint/4.0.x (e042875) will increase coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           maint/4.0.x    #1117   +/-   ##
============================================
  Coverage        91.75%   91.76%           
============================================
  Files              101      101           
  Lines            12380    12380           
  Branches          2423     2423           
============================================
+ Hits             11359    11360    +1     
+ Misses             694      693    -1     
  Partials           327      327           

Impacted Files	Coverage Δ
nibabel/gifti/gifti.py	86.47% <0.00%> (-1.48%)	⬇️
nibabel/viewers.py	96.14% <0.00%> (+0.64%)	⬆️
nibabel/freesurfer/mghformat.py	92.93% <0.00%> (+1.48%)	⬆️

---

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 e042875...d1b66c5. Read the comment docs.

[effigies]

Pre-release failures are related to numpy/numpy#21437. Will address separately.