Use internal build version for release SWIs

Software image version for release SWIs only contains the version and not the
changenum.

src/pytest_netdut/factories.py

@@ -163,7 +163,14 @@ def _os_version(request):
         ssh = request.getfixturevalue(f"{name}_ssh")
         assert ssh.cli_flavor in {"eos", "mos"}
         output = ssh.sendcmd("show version", timeout=300)
-        matcher = re.search(r"Software image version: (\S*)", output)
+        if ssh.cli_flavor == "mos":
+            matcher = re.search(r"Software image version: (\S*)", output)
+        else:
+            # On release SWIs the "Sofware image version" only contains the version, e.g.
+            #   Software image version: 4.31.0F
+            #   Architecture: x86_64
+            #   Internal build version: 4.31.0F-33797590.4310F
+            matcher = re.search(r"Internal build version: (\S*)", output)
         logging.info("Got OS version: %s", matcher.group(1))
         yield matcher.group(1)