AP_NavEKF3: record the anchored compass yaw fusion

On the ground with EK3_MAG_CAL 7 the compass yaw is fused as an anchor
before 3-axis fusion. If the 3-axis fusion then fails its innovation
check, last_mag_yaw_fuse_ms was not refreshed although a yaw update
was applied.

libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp

@@ -563,6 +563,7 @@ void NavEKF3_core::SelectMagFusion()
                 // bad_yaw covers the case where FinishFusion skipped the update
                 if (yawAnchored && !faultStatus.bad_yaw) {
                     magFusionSel = MagFuseSel::FUSE_MAG_ANCHORED;
+                    last_mag_yaw_fuse_ms = imuSampleTime_ms;
                 }
             }
             // if we are not doing aiding with earth relative observations (eg GPS) then the declination is