Fix configuration after gnmi test (sonic-net#19150)

What is the motivation for this PR?
Some end to end tests failed because the configuration is wrong after gnmi test.

How did you do it?
Run "config save" command to make sure configuration is persistent.

How did you verify/test it?
Run gnmi end to end test and check configuration.

Signed-off-by: Yael Tzur <ytzur@nvidia.com>

Author: ganglyu

tests/gnmi/conftest.py

@@ -237,6 +237,9 @@ def setup_gnmi_server(duthosts, rand_one_dut_hostname, localhost, ptfhost):
 
     # Rollback configuration
     rollback(duthost, SETUP_ENV_CP)
+    # Save the configuration
+    cmd = "config save -y"
+    duthost.shell(cmd, module_ignore_errors=True)
     recover_cert_config(duthost)