Use consistent variable names for IP examples (#4679)

Author: lb7

packages/docs/content/api.mdx

@@ -455,10 +455,10 @@ z.iso.time({ precision: 3 }); // HH:MM:SS.sss (millisecond precision)
 
 ```ts
 const ipv4 = z.ipv4();
-v4.parse("192.168.0.0"); // ✅
+ipv4.parse("192.168.0.0"); // ✅
 
 const ipv6 = z.ipv6();
-v6.parse("2001:db8:85a3::8a2e:370:7334"); // ✅
+ipv6.parse("2001:db8:85a3::8a2e:370:7334"); // ✅
 ```
 
 ### IP blocks (CIDR)