fix(ci): use workflow-scoped token for Bioconda publish

The Bioconda publish job fails when pushing the version bump branch to the `nextstrain/bioconda-recipes` fork:

```
refusing to allow a Personal Access Token to create or update workflow
`.github/workflows/PR.yml` without `workflow` scope
```

GitHub requires the `workflow` scope on any token that pushes a ref whose tree contains `.github/workflows/` files. The fork inherits these files from upstream `bioconda/bioconda-recipes`, so the scope is required even though our commit only touches `recipes/nextclade/meta.yaml`.

Switch from `GH_TOKEN_NEXTSTRAIN_BOT_REPO` to `GH_TOKEN_NEXTSTRAIN_BOT_WORKFLOW`, which carries the `workflow` scope in addition to the same permissions as the previous token.

- CI failure: https://github.com/nextstrain/nextclade/actions/runs/24439124069/job/71399868528
- Discussion: https://bedfordlab.slack.com/archives/C01LCTT7JNN/p1776233996707089

Author: ivan-aksamentov

.github/workflows/bioconda.yml

@@ -44,7 +44,7 @@ jobs:
         id: bump-version
         shell: bash
         run: |
-          export GITHUB_TOKEN="${{ secrets.GH_TOKEN_NEXTSTRAIN_BOT_REPO }}"
+          export GITHUB_TOKEN="${{ secrets.GH_TOKEN_NEXTSTRAIN_BOT_WORKFLOW }}"
 
           mkdir -p "${HOME}/bin"
           export PATH="${HOME}/bin:${PATH}"