Improve HOTEND OFFSET Z display precision to 3 (#11686)

Marlin/src/module/configuration_store.cpp

         SERIAL_ECHOPAIR_P(port, "  M218 T", (int)e);
         SERIAL_ECHOPAIR_P(port, " X", LINEAR_UNIT(hotend_offset[X_AXIS][e]));
         SERIAL_ECHOPAIR_P(port, " Y", LINEAR_UNIT(hotend_offset[Y_AXIS][e]));
-        SERIAL_ECHOPAIR_P(port, " Z", LINEAR_UNIT(hotend_offset[Z_AXIS][e]));
+        SERIAL_ECHO_P(port, " Z");
+        SERIAL_ECHO_F_P(port, LINEAR_UNIT(hotend_offset[Z_AXIS][e]), 3);
         SERIAL_EOL_P(port);
       }
     #endif