[dev]: replace `hub` with `gh`

[jsjoeio]

As @oxy pointed out, we're currently using a mix of hub and gh in our build scripts.

• https://github.com/cdr/code-server/blob/main/ci/build/release-github-assets.sh#L18
• https://github.com/cdr/code-server/blob/main/ci/build/release-github-draft.sh#L10

We should replace hub with gh and use one consistently throughout the codebase.

Related:

• dev: add release:prep script #2952