TrackerMeasurementFromHits: fix time component of covariance (#1666)

This value is not used yet, but should be squared, in principle.

### Briefly, what does this PR introduce?


### What kind of change does this PR introduce?
- [x] Bug fix (issue #__)
- [ ] New feature (issue #__)
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
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### Does this PR introduce breaking changes? What changes might users
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### Does this PR change default behavior?

src/algorithms/tracking/TrackerMeasurementFromHits.cc

@@ -125,7 +125,7 @@ namespace eicrecon {
             meas2D.setLoc({static_cast<float>(pos[0]),static_cast<float>(pos[1])});                     // 2D location on surface
             meas2D.setTime(hit.getTime());                     // Measurement time
             // fixme: no off-diagonal terms. cov(0,1) = cov(1,0)??
-            meas2D.setCovariance({cov(0,0),cov(1,1),hit.getTimeError(),cov(0,1)}); // Covariance on location and time
+            meas2D.setCovariance({cov(0,0), cov(1,1), hit.getTimeError() * hit.getTimeError(), cov(0,1)}); // Covariance on location and time
             meas2D.addToWeights(1.0);                             // Weight for each of the hits, mirrors hits array
             meas2D.addToHits(hit);
         }