Update MuonEventTPCnv reference files after !31114
Since !31114 (merged) was merged into 21.3, the MuonEventTPCnv_20.1.7.2
unit
test has been failing due to the fact that the reference file was not
updated after the TPCnv bug was fixed.
This merge request also backports a fix from master to allow TPCnv unit test reference files to be read from cvmfs.