test: LIBP2P_TCP_MUX: true

this re-enabled TCP muxing

(if sharness fails due to timeout, we have bug related to
libp2p.ShareTCPListener() somehow)

.github/workflows/sharness.yml

@@ -52,7 +52,7 @@ jobs:
           TEST_EXPENSIVE: 1
           IPFS_CHECK_RCMGR_DEFAULTS: 1
           CONTINUE_ON_S_FAILURE: 1
-          LIBP2P_TCP_MUX: false # TODO
+          LIBP2P_TCP_MUX: true # TODO
           # increasing parallelism beyond 10 doesn't speed up the tests much
           PARALLEL: ${{ github.repository == 'ipfs/kubo' && 10 || 3 }}
       - name: Upload coverage report