fix: linux-amd64-e2e job timeout issue

Assume etcd-io#16916 as baseline. The E2E takes `1395.082s`.

* etcd-io#16988

It introduced `TestAuthority` which takes `18.39s`.
And after etcd-io#16997, it takes `50.05s`.

* etcd-io#16995

It introduced `TestInPlaceRecovery` which takes `17.37s`.

* etcd-io#17144

  - New `TestHTTPHealthHandler` takes `29.9s`
  - New `TestHTTPLivezReadyzHandler` takes `35.20s`

* etcd-io#17173

  - New `TestMemberReplace` takes `7.55s`.

Ideally, it should increase `140.07s`. It's not larger than `1800s`
timeout value.

However, we run E2E cases 3 times. By default, we run E2E cases with
`-cpu 1,2,4`. That means that we run 3 times.

`1395.082s` + `140.07s * 3` = `1815.292s` > `1800s`

```bash
$ go help testflag

 -count n
            Run each test, benchmark, and fuzz seed n times (default 1).

            If -cpu is set, run n times for each GOMAXPROCS value.
            Examples are always run once. -count does not apply to
            fuzz tests matched by -fuzz.
```

I don't think we should run E2E with different GOMAXPROCS value. All the
`TestXYZ` are used to control etcd process and we don't set GOMAXPROCS
env to etcd process.

Set `CPU=4` to align with main and release/3.5.

Closes: etcd-io#17241

Signed-off-by: Wei Fu <[email protected]>

.github/workflows/tests.yaml

@@ -66,7 +66,7 @@ jobs:
             PASSES='build grpcproxy' CPU='4' RACE='true' ./test
             ;;
           linux-amd64-e2e)
-            GOARCH=amd64 make test-e2e-release
+            GOARCH=amd64 CPU='4' make test-e2e-release
             ;;
           linux-386-unit)
             GOARCH=386 make test-unit