Fix code linter error

The error was:
```
 src/pcluster/resources/batch/docker/alinux2/Dockerfile
   ❯❯❱ dockerfile.security.missing-user-entrypoint.missing-user-entrypoint
          By not specifying a USER, a program in the container may run as 'root'. This is a security hazard.
          If an attacker can control a process running as root, they may have control over the container.
          Ensure that the last USER in a Dockerfile is a USER other than 'root'.
          Details: https://sg.run/k281

           ▶▶┆ Autofix ▶ USER non-root ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]
           60┆ ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]

    src/pcluster/resources/batch/docker/alinux2023/Dockerfile
   ❯❯❱ dockerfile.security.missing-user-entrypoint.missing-user-entrypoint
          By not specifying a USER, a program in the container may run as 'root'. This is a security hazard.
          If an attacker can control a process running as root, they may have control over the container.
          Ensure that the last USER in a Dockerfile is a USER other than 'root'.
          Details: https://sg.run/k281

           ▶▶┆ Autofix ▶ USER non-root ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]
           60┆ ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]
```

Signed-off-by: Hanwen <[email protected]>

cli/src/pcluster/resources/batch/docker/alinux2/Dockerfile

@@ -57,4 +57,4 @@ ENV PATH "/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/usr/lib6
 # expose ssh port
 EXPOSE 22
 
-ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]
+USER root ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]

cli/src/pcluster/resources/batch/docker/alinux2023/Dockerfile

@@ -57,4 +57,4 @@ ENV PATH "/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/usr/lib6
 # expose ssh port
 EXPOSE 22
 
-ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]
+USER root ENTRYPOINT ["/parallelcluster/bin/entrypoint.sh"]