fix(ci): fetch previous tag from git instead of API (#952)
fix(ci): fetch previous tag from git instead of API (#952)

Previously the release info script would query the GitHub HTTP API and retrieve
the latest "Release" (git tag) published.
The latest "Release" could (likely) be for a different `release-*` branch or
even `master` rather than the previous tag on the same branch as the new
tag.
This resulted in "Release" changelogs containing commits that dont
exist in the tags history.

By instead querying git itself we can fetch the previous tag in history
and then generate an accurate changelog, eg: between `v1.7.4` and
`v1.7.3` rather than potentially `v1.7.4` and `v1.10.0`.

Run script through `shellcheck` and `shfmt`.
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