GasLiftSingleWell: pull fmt in impl file

it is not used in the interface.
no real change to the code as such, but it better reflects the use.

opm/simulators/wells/GasLiftSingleWell.hpp

@@ -30,7 +30,6 @@
 #include <optional>
 #include <vector>
 #include <utility>
-#include <fmt/format.h>
 
 namespace Opm
 {

opm/simulators/wells/GasLiftSingleWell_impl.hpp

@@ -17,6 +17,8 @@
   along with OPM.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <fmt/format.h>
+
 namespace Opm {
 
 template<typename TypeTag>