Tests: Capture Bccb determinant threshold for MSVC

libeigen/eigen!3056

contrib/test/structured_bccb.cpp

diff --git a/contrib/test/structured_bccb.cpp b/contrib/test/structured_bccb.cpp
index d5aa38e..aa25227 100644
--- a/contrib/test/structured_bccb.cpp
+++ b/contrib/test/structured_bccb.cpp
@@ -601,7 +601,7 @@
   // the true determinant lead^nLead * rest^(N - nLead) is representable. The
   // generator is recovered through the dense inverse 2-D DFT matrices,
   // independently of the implementation under test.
-  auto makeOperator = [n2, n1](double lead, double rest) {
+  auto makeOperator = [n2, n1, nLead](double lead, double rest) {
     CMat S(n2, n1);
     for (Index k1 = 0; k1 < n1; ++k1)
       for (Index k2 = 0; k2 < n2; ++k2) S(k2, k1) = Complex(k1 * n2 + k2 < nLead ? lead : rest);