facts: fix tests for getent based server.Groups

Author: bauen1

pyinfra/facts/server.py

@@ -420,6 +420,9 @@ def command(self):
         # all groups / users, in which case only the local groups will be returned
         return "getent group"
 
+    def requires_command(self) -> str:
+        return "getent"
+
     default = list
 
     def process(self, output) -> list[str]:

tests/facts/server.Groups/groups.json

@@ -1,5 +1,6 @@
 {
-    "command": "cat /etc/group",
+    "command": "getent group",
+    "requires_command": "getent",
     "output": [
         "lpadmin:x:114:vagrant",
         "sambashare:x:115:vagrant",