[CI] Also test against Dune 2.7

Even for the master branch I'd like to know that this kinda works against the 2.7 release, because that is what people using packages have.

dune/elasticity/materials/localintegralenergy.hh

@@ -2,7 +2,10 @@
 #define DUNE_ELASTICITY_MATERIALS_LOCALINTEGRALENERGY_HH
 
 #include <dune/common/fmatrix.hh>
+#include <dune/common/version.hh>
+#if DUNE_VERSION_NEWER(DUNE_COMMON, 2, 8)
 #include <dune/common/transpose.hh>
+#endif
 
 #include <dune/geometry/quadraturerules.hh>
 
@@ -77,7 +80,14 @@ energy(const LocalView& localView,
 
     // compute gradients of base functions
     for (size_t i=0; i<jacobians.size(); ++i)
+#if DUNE_VERSION_NEWER(DUNE_COMMON, 2, 8)
       jacobians[i] = jacobians[i] * transpose(geometryJacobianIT);
+#else
+    {
+      auto referenceJacobian = jacobians[i];
+      geometryJacobianIT.mv(referenceJacobian[0], jacobians[i]);
+    }
+#endif
 
     // Deformation gradient
     FieldMatrix<field_type,gridDim,gridDim> deformationGradient(0);