Rename previously-named e2e workflow to external-app for consiste…

…ncy (#311)

## Problem

This is a fast-follow from [the PR that introduced the external app
testing for Edge
runtimes](#304).
We just need to rename the GH workflow to match the rest of the
files/code in the client, which we couldn't do previously w/o creating a
new workflow and merging it to `main`.

## Type of Change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [ ] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

.github/workflows/testing.yml

@@ -220,7 +220,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Run external app tests
-        uses: ./.github/actions/e2e-testing/edge
+        uses: ./.github/actions/external-app/edge
         with:
           vercel-token: ${{ secrets.VERCEL_TOKEN }}
           PINECONE_API_KEY: ${{ secrets.PINECONE_API_KEY }}