Fix lint error from let_underscore_lock (#228)

* Fix lint error from let_underscore_lock

* Nightly says to go back to ok_or_else

a2de8a9 did this because of the previous clippy error, and now it says hey go back to what it was :D

There is no way to make both versions happy, so for now I added allow() to suppress the stable one.

src/value.rs

@@ -37,7 +37,8 @@ pub enum Type {
 /// We use manual tagging, because <https://github.com/serde-rs/serde/issues/610>.
 impl Type {
     pub fn from_tag(tag: u8) -> Result<Type, DataError> {
-        Type::from_primitive(tag).ok_or(DataError::UnknownType(tag))
+        #![allow(clippy::unnecessary_lazy_evaluations)]
+        Type::from_primitive(tag).ok_or_else(|| DataError::UnknownType(tag))
     }
 
     #[allow(clippy::wrong_self_convention)]

tests/manager.rs

@@ -26,7 +26,7 @@ use rkv::{
 fn test_simple() {
     type Manager = rkv::Manager<LmdbEnvironment>;
 
-    let _ = Manager::singleton().write().unwrap();
+    let _unused = Manager::singleton().write().unwrap();
 }
 
 /// Test that a manager can be created with simple type inference.
@@ -35,7 +35,7 @@ fn test_simple() {
 fn test_simple_safe() {
     type Manager = rkv::Manager<SafeModeEnvironment>;
 
-    let _ = Manager::singleton().write().unwrap();
+    let _unused = Manager::singleton().write().unwrap();
 }
 
 /// Test that a shared Rkv instance can be created with simple type inference.