Dynare++: fix check for QZ eigenvalue criterium

The criterium was previously incorrectly applied to the square absolute value
of eigenvalues. Rather apply it to the absolute value itself (as now done in
Dynare).

Ref #1632

(manually cherry picked from commit 8ebcd7ca)
4 jobs for 4.5 in 332 minutes and 21 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #2378
build_binaries

00:07:30

passed #2379
build_doc

00:02:21

 
  Test
failed #2380
testsuite_matlab

00:49:25

passed #2381
testsuite_octave_auto

05:24:50

 
Name Stage Failure
failed
testsuite_matlab Test
tests/*.m.log: found 31 matching files             
tests/*.m.trs: found 31 matching files

tests/*/*.m.log: found 222 matching files

tests/*/*.m.trs: found 222 matching files

tests/*/*/*.m.log: found 104 matching files

tests/*/*/*.m.trs: found 104 matching files

tests/run_test_matlab_output.txt: found 1 matching files

Uploading artifacts to coordinator... ok
id=2380 responseStatus=201 Created token=264UMoMh
ERROR: Job failed: exit status 1