[test][1p] Use class template deduction for type of LinearPDESolve
According to https://en.cppreference.com/w/cpp/compiler_support this should work with GCC 7 & Clang 5. But we should test this is bit.
According to https://en.cppreference.com/w/cpp/compiler_support this should work with GCC 7 & Clang 5. But we should test this is bit.