MuonReadoutGeometryR4: Fix compilation with clang.

A streamer operator should be in the namespace of the object it's streaming. Missing override keyword.

This merge request affects 1 package:

• MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4

This merge request affects 3 files:

• MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/MdtReadoutElement.h
• MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/MuonReadoutElement.h
• MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/src/MdtReadoutElement.cxx

Adding @rosati ,@stavrop ,@jojungge ,@apsallid ,@pscholer as watchers

added MuonSpectrometer master review-pending-level-1 labels

CI Result SUCCESS (hash bead1a70)

	Athena
externals
cmake
make
tests

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Athena: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 70883]

added review-approved label and removed review-pending-level-1 label

CHanges and CI look fine. Approving.

Kira (L1)

merged

mentioned in commit 41ae53a4

added sweep:ignore label