Fix explicit lifetimes for consts (#467)

Introduce explicit lifetimes for `ToSchema` and `ToResponse` lifetime
variables to make library build in Rust 1.60. Automatic lifetime elision
for const seems to be available from Rust 1.64 onwards and we want to
make sure this lib builds in Rust 1.60 as well.

utoipa-gen/src/component/schema.rs

@@ -51,7 +51,7 @@ pub struct Schema<'a> {
 }
 
 impl<'a> Schema<'a> {
-    const TO_SCHEMA_LIFETIME: &str = "'__s";
+    const TO_SCHEMA_LIFETIME: &'static str = "'__s";
     pub fn new(
         data: &'a Data,
         attributes: &'a [Attribute],

utoipa-gen/src/path/response/derive.rs

@@ -31,7 +31,7 @@ pub struct ToResponse<'r> {
 }
 
 impl<'r> ToResponse<'r> {
-    const LIFETIME: &str = "'__r";
+    const LIFETIME: &'static str = "'__r";
 
     pub fn new(
         attributes: Vec<Attribute>,