deploy: fix duplicate env block

https://github.com/git/git-scm.com/actions/runs/11156892349 failed with
this error message:

	⨂ Invalid workflow file: .github/workflows/deploy.yml#L29
	The workflow is not valid. .github/workflows/deploy.yml (Line: 29, Col: 9): 'env' is already defined

The fix is easy: merge the two `env` blocks into a single one.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

.github/workflows/deploy.yml

@@ -23,9 +23,7 @@ jobs:
         uses: ./.github/actions/deploy-to-github-pages
       - name: Purge Cloudflare cache
         env:
+          CLOUDFLARE_ZONE: ${{ secrets.CLOUDFLARE_ZONE }}
           CLOUDFLARE_TOKEN: ${{ secrets.CLOUDFLARE_TOKEN }}
         if: env.CLOUDFLARE_TOKEN != ''
         uses: jakejarvis/cloudflare-purge-action@v0.3.0
-        env:
-          CLOUDFLARE_ZONE: ${{ secrets.CLOUDFLARE_ZONE }}
-          CLOUDFLARE_TOKEN: ${{ secrets.CLOUDFLARE_TOKEN }}