fix: never let root read the SSH configuration from stdin

A driver gains root with sudo -S and puts the password in front of stdin.
A sudo that does not prompt -- NOPASSWD, a cached timestamp -- leaves it
there, and the cat under sudo wrote it into the drop-in as its first line.
Seen on the first real run (NetOrk/netork#1027): sshd -t rejected the file
and the rollback removed it, but the password was in a 0644 file for a
moment and in the error the caller showed.

The content now goes without privilege to a mktemp file only the login user
can read; root installs that file (mode 644, root-owned) and removes it.
The fake host in the tests prepends the password to every privileged stdin,
as a non-prompting sudo does.

Bumps to 4.5.1. NetOrk/netork#1027, NetOrk/netork#1029

napalm_device_types/ssh_server.py

@@ -285,11 +285,28 @@ class OpenSshServerMixin:
         return result.stdout if result.exit_code == 0 else None
 
     def _ssh_write(self, path: str, content: str) -> None:
-        script = (
-            f'tmp={quote(path + ".netork-tmp")} && cat > "$tmp" && chmod 644 "$tmp"'
-            f' && mv -f -- "$tmp" {quote(path)} || {{ s=$?; rm -f -- "$tmp"; exit $s; }}'
+        """Replace *path* with *content*, as root, without root reading stdin.
+
+        A driver gains root with ``sudo -S`` and puts the password in front of
+        stdin. A sudo that does not prompt -- NOPASSWD, a cached timestamp --
+        leaves it there, and a ``cat`` under sudo writes it into the file. So the
+        content goes, without privilege, to a file only the login user can read;
+        root then installs that file (mode 644, owned by root) and removes it.
+        """
+        staged = self.run_command(
+            'umask 077 && t=$(mktemp /tmp/netork-ssh.XXXXXX) && cat > "$t" && printf %s "$t"',
+            privileged=False,
+            timeout=30,
+            stdin=content.encode(),
+        )
+        tmp = staged.stdout.strip()
+        if staged.exit_code != 0 or not tmp.startswith("/tmp/netork-ssh."):
+            raise RuntimeError(f"could not stage {path}: {(staged.stderr or staged.stdout).strip()}")
+        part = path + ".netork-tmp"
+        result = self._ssh_run(
+            f"install -m 644 -- {quote(tmp)} {quote(part)} && mv -f -- {quote(part)} {quote(path)};"
+            f" s=$?; rm -f -- {quote(tmp)} {quote(part)}; exit $s"
         )
-        result = self._ssh_run(script, stdin=content.encode())
         if result.exit_code != 0:
             raise RuntimeError(f"could not write {path}: {(result.stderr or result.stdout).strip()}")