[v0.6] Revert "Bump metrics.version from 4.2.19 to 4.2.20"

[li-boxuan]

This reverts commit 58294e4, which causes a few test failure consistently.

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[li-boxuan]

I'll merge this with CTR as this is simply a revert of dependency.

[FlorianHockmann]

My bad, the backport didn't just update from 4.2.19 to 4.2.20, but updated from 4.1.33 which indicates already that 4.2 is problematic for v0.6 as we then skipped backports for this dependency already earlier.
Sorry for the trouble and thanks for fixing this!