Suppress or deal with messages in tests

[IndrajeetPatil]

Related to easystats/easystats#343

Current output:

Gu & Wahba 4 term additive model
Registered S3 methods overwritten by 'ivreg':
  method              from
  anova.ivreg         AER 
  hatvalues.ivreg     AER 
  model.matrix.ivreg  AER 
  predict.ivreg       AER 
  print.ivreg         AER 
  print.summary.ivreg AER 
  summary.ivreg       AER 
  terms.ivreg         AER 
  update.ivreg        AER 
  vcov.ivreg          AER 
Compiling Stan program...
Start sampling
boundary (singular) fit: see help('isSingular')
boundary (singular) fit: see help('isSingular')
boundary (singular) fit: see help('isSingular')
boundary (singular) fit: see help('isSingular')
boundary (singular) fit: see help('isSingular')
boundary (singular) fit: see help('isSingular')
Error in .Call("FreeADFunObject", ptr, PACKAGE = DLL) : 
  "FreeADFunObject" not available for .Call() for package "glmmTMB"
Calls: <Anonymous>
Registered S3 methods overwritten by 'polspline':
  method               from     
  plot.logspline       logspline
  plot.oldlogspline    logspline
  print.logspline      logspline
  print.oldlogspline   logspline
  summary.logspline    logspline
  summary.oldlogspline logspline
boundary (singular) fit: see help('isSingular')
Fitting a multivariate glmer model.

Please note the warmup may be much slower than later iterations!
Registered S3 methods overwritten by 'AER':
  method              from 
  print.ivreg         ivreg
  print.summary.ivreg ivreg
  summary.ivreg       ivreg
  vcov.ivreg          ivreg
  bread.ivreg         ivreg
  estfun.ivreg        ivreg
  hatvalues.ivreg     ivreg
  predict.ivreg       ivreg
  anova.ivreg         ivreg
  terms.ivreg         ivreg
  model.matrix.ivreg  ivreg
  update.ivreg        ivreg

[strengejacke]

I think this can be closed. I'm checking unnecessary messages every now and then.