fix: enable pipefail mode for grpcproxy test

By default, the pipefail is disabled. For instance, the commands should
return 1 as exit code, but we get zero. After pipefail enabled, it's
back to normal.

```bash
$ ( echo hello; exit 1 ) | tee 2>&1
hello
$ echo $?
0

$ set -o pipefail
$ ( echo hello; exit 122 ) | tee 2>&1
hello
$ echo $?
122
```

And the test.log is used to grep the error from a ton of messages. So
that we should `set +e` and set it back after egrep.

fixes: etcd-io#15487

Signed-off-by: Wei Fu <fuweid89@gmail.com>

.github/workflows/tests.yaml

@@ -58,8 +58,12 @@ jobs:
             GO_BUILD_FLAGS='-v' GOARCH=s390x ./build
             ;;
           linux-amd64-grpcproxy)
+            set -o pipefail; set +e;
             PASSES='build grpcproxy' CPU='4' RACE='true' ./test 2>&1 | tee test.log
-            ! egrep "(--- FAIL:|DATA RACE|panic: test timed out|appears to have leaked)" -B50 -A10 test.log
+            ecode=$?
+            egrep "(--- FAIL:|DATA RACE|panic: test timed out|appears to have leaked)" -B50 -A10 test.log
+            set -e
+            exit ${ecode}
             ;;
           linux-386-unit)
             GOARCH=386 PASSES='unit' ./test