find_predictors() with multiple strata() variables in clogit()

[strengejacke]

Fixes #821

[codecov]

Codecov Report

Merging #822 (aab87e8) into main (6f53383) will increase coverage by 0.05%.
Report is 2 commits behind head on main.
The diff coverage is 92.30%.

❗ Current head aab87e8 differs from pull request most recent head 90e0e6f. Consider uploading reports for the commit 90e0e6f to get more accurate results

@@            Coverage Diff             @@
##             main     #822      +/-   ##
==========================================
+ Coverage   54.95%   55.00%   +0.05%     
==========================================
  Files         124      124              
  Lines       15370    15381      +11     
==========================================
+ Hits         8446     8461      +15     
+ Misses       6924     6920       -4     

Files	Coverage Δ
R/color_if.R	0.00% <ø> (ø)
R/find_predictors.R	80.15% <100.00%> (+0.78%)	⬆️
R/get_varcov.R	25.76% <85.71%> (+2.02%)	⬆️