probe_eddy_current: Allow "tap" depress of as little as 30um

There have been some reports of the sanity check throwing an error
when the bed is depressed just under 50um.  For now, increase the
valid depress range to avoid unnecessary errors.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/probe_eddy_current.py

@@ -726,9 +726,9 @@ class EddyTap:
         if slope >= 0. or slope2 < 0.:
             self._error_detect("invalid free air slope (s=%.6f s2=%.6f)"
                                % (slope, slope2))
-        if z_contact - min_z < 0.050 or z_contact - min_z > 0.250:
+        if z_contact - min_z < 0.030 or z_contact - min_z > 0.250:
             self._error_detect("invalid depress distance (%.6f vs %.6f:%.6f)"
-                               % (z_contact - min_z, 0.050, 0.250))
+                               % (z_contact - min_z, 0.030, 0.250))
         # Report probe position
         trig_idx = len(data)-1
         while trig_idx > 0 and data[trig_idx-1][1][2] > z_contact: