Fix panic in JSONB decoder on invalid version byte (#4158)

* Fix panic in JSONB decoder on invalid version byte

Replace assert_eq! with proper error handling to prevent panic on
untrusted database input. The Decode trait contract requires returning
Result<T, Error>, but the assertion would cause a panic instead.

This issue was discovered through fuzzing and can be triggered by:
- Malformed JSONB data in the database
- Database corruption
- Future PostgreSQL versions with different JSONB formats

The fix replaces the assertion with a conditional check that returns
an appropriate error, maintaining the Decode trait contract and
allowing applications to handle the error gracefully.

Signed-off-by: Jared Reyes <jaredreyespt@gmail.com>

* Fix formatting

Signed-off-by: Jared Reyes <jaredreyespt@gmail.com>

---------

Signed-off-by: Jared Reyes <jaredreyespt@gmail.com>

Author: jrey8343

sqlx-postgres/src/types/json.rs

@@ -85,11 +85,12 @@ where
         let mut buf = value.as_bytes()?;
 
         if value.format() == PgValueFormat::Binary && value.type_info == PgTypeInfo::JSONB {
-            assert_eq!(
-                buf[0], 1,
-                "unsupported JSONB format version {}; please open an issue",
-                buf[0]
-            );
+            // Check JSONB version byte - PostgreSQL currently only supports version 1
+            if buf[0] != 1 {
+                return Err(
+                    format!("unsupported JSONB format version {} (expected 1)", buf[0]).into(),
+                );
+            }
 
             buf = &buf[1..];
         }