fix(ci): semantic-release workflow for v9 releases (#1082)

## 🧰 Changes

sets up the `semantic-release` configuration so we can properly maintain
v9 releases.

further reading:
https://semantic-release.gitbook.io/semantic-release/usage/workflow-configuration#maintenance-branches

outstanding work:

- [x] make sure that the major tag is only set on the `main` branch
release (e.g., if `v10.0.1` is being published then the major tagging
step should run, but if we're publishing a `v9.0.1` release then the
major tagging step should **not** run)
- [x] **(do this right before merging)** make sure a `v9` branch is
created and it's pointing to the same commit as the `v9` tag
- [ ] **(do this right after merging)** if the release was successfully
published to the `v9` branch, then delete the `v9` tag

## 🧬 QA & Testing

we truly won't know if this works until it's merged 🫠 but that's why we
have a `next` branch right?

.github/workflows/release.yml

@@ -4,6 +4,7 @@ on:
     branches:
       - main
       - next
+      - v9
 
 env:
   REGISTRY: ghcr.io

.releaserc.yml

@@ -3,6 +3,8 @@ branches:
   - name: main
   - name: next
     prerelease: true
+  - name: v9
+    channel: 9.x
 
 plugins:
   - '@semantic-release/commit-analyzer'