ci: Revamp the QNS CI action timeout (#2361)

* ci: Revamp the QNS CI action timeout

It seems that the `TIMEOUT` env variable applies to all steps?

* Simpler

Author: larseggert

.github/workflows/qns.yml

@@ -23,7 +23,6 @@ permissions:
 env:
   LATEST: neqo-latest
   DELIM: ' vs. '
-  TIMEOUT: 30
 
 jobs:
   docker-image:
@@ -149,7 +148,7 @@ jobs:
 
       # TODO: Replace once https://github.com/quic-interop/quic-interop-runner/pull/356 is merged.
       - uses: ./.github/actions/quic-interop-runner
-        timeout-minutes: ${{ fromJSON(env.TIMEOUT) }}
+        timeout-minutes: 20
         with:
           client: ${{ steps.depair.outputs.client }}
           server: ${{ steps.depair.outputs.server }}