[9.10] Various post-release fixes

• Bump the haddock submodule to bump its version number, as this was seemingly lost (see #24827)
• Update ghcup-metadata to reflect upstream's preferences
• Fix the name of setBacktraceMechanismState in the base changelog entry
• Fix upload script to ensure that gzip files are hashed.
• Backport fix for #24853 (closed)