Only include the multiplication of a ScaledIdentityMatrix with another...

Only include the multiplication of a ScaledIdentityMatrix with another FieldMatrix if dune common is older or equal 2.8

@osander: can you have a look?

So what bug is this fixing?

After pulling this commit (https://gitlab.dune-project.org/core/dune-common/-/commit/923d1c75d13ccee3f2d8d54db0138795807c7e35) from dune-common master, the program simofoxshell in dune-gfe did not build anymore because the multiplication of a ScaledIdentityMatrix and a FieldMatrix were defined twice.

mentioned in commit e00a65a2

merged