chore: allow renamed and removed lints on docs build (#2344)

Currently, the Netlify docs are failing because of a warning that one of
the lints we explicitly enable is no longer a warning on nightly but
becoming a hard error. This is because the docs are built on nightly
with `-D warnings`, which denies all warnings...which seems not ideal.

For now, let's not remove that lint from the `deny` list, as it's still
a valid lint on stable. Instead, this PR explicitly allows that lint on
the docs build.

Author: hawkw

netlify.toml

@@ -8,6 +8,7 @@
 [build.environment]
   RUSTDOCFLAGS="""
     -D warnings \
+    --force-warn renamed-and-removed-lints \
     --cfg docsrs \
     --cfg tracing_unstable
     """