revert: remove test code that shouldn't have been merged (#782)

Author: seanmonstar

src/version.rs

@@ -43,14 +43,13 @@ impl Version {
 }
 
 #[derive(PartialEq, PartialOrd, Copy, Clone, Eq, Ord, Hash)]
-#[non_exhaustive]
 enum Http {
     Http09,
     Http10,
     Http11,
     H2,
     H3,
-    //__NonExhaustive,
+    __NonExhaustive,
 }
 
 impl Default for Version {
@@ -70,7 +69,7 @@ impl fmt::Debug for Version {
             Http11 => "HTTP/1.1",
             H2 => "HTTP/2.0",
             H3 => "HTTP/3.0",
-            //__NonExhaustive => unreachable!(),
+            __NonExhaustive => unreachable!(),
         })
     }
 }