deps/api: Bump `prometheus_metrics_model` -> 0.6.0

[dependency-envoy[bot]]

Created by Envoy dependency bot for @phlax

Fix #32454

Signed-off-by: dependency-envoy[bot] <148525496+dependency-envoy[bot]@users.noreply.github.com>

[repokitteh-read-only[bot]]

CC @envoyproxy/dependency-shepherds: Your approval is needed for changes made to (bazel/.*repos.*\.bzl)|(bazel/dependency_imports\.bzl)|(api/bazel/.*\.bzl)|(.*/requirements\.txt)|(.*\.patch). envoyproxy/dependency-shepherds assignee is @moderation

:cat:

Caused by: https://github.com/envoyproxy/envoy/pull/32542 was opened by dependency-envoy[bot].

see: more, trace.

[moderation]

/lgtm deps