For some reason httpconv seems to have disappeared from 1.21, which
results in a 1.21 runtime with 1.20 semconv/httpconv which seems to
break some things.
For now, this rolls the OTEL dependencies back to 1.20 which should fix
the observability issues. We'll need to take a look at how to upgrade
safely and correctly in the future.
Relates to #2503.