verification.py updates

[GertjanBisschop]

Last updates to verification,py to stop pandas from complaining and keep pyslim happy.
Also, test_dtwf_vs_coalescent_single_forced_recombination was only set to a single replicate. Have rectified this. This is not a computationally expensive test.

[codecov]

Codecov Report

Merging #2236 (ce6964a) into main (2c5fe55) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2236   +/-   ##
=======================================
  Coverage   91.52%   91.52%           
=======================================
  Files          20       20           
  Lines       11337    11337           
  Branches     2304     2304           
=======================================
  Hits        10376    10376           
  Misses        523      523           
  Partials      438      438           

Flag	Coverage Δ
C	91.52% <ø> (ø)
python	98.70% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2c5fe55...ce6964a. Read the comment docs.