Fix compiler warning regarding future errors

As preparation for an upcoming Rust compiler release, the following
warning was generated and needed to be fixed:

    warning: this function depends on never type fallback being `()`
       --> src/main.rs:247:1
        |
    247 | fn bump(version: String) -> Result<()> {
        | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
        = note: for more information, see issue #123748 <rust-lang/rust#123748>
        = help: specify the types explicitly
    note: in edition 2024, the requirement `!: LuaUserData` will fail
       --> src/main.rs:268:22
        |
    268 |                     .call(())
        |                      ^^^^
        = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default

src/main.rs

@@ -265,7 +265,7 @@ fn bump(version: String) -> Result<()> {
         if let Some(hooks) = &hooks {
             if let Some(pre_func) = hooks.get("pre_func") {
                 pre_func
-                    .call(())
+                    .call::<_, ()>(())
                     .map_err(|source| Error::LuaPreFuncFailed { source })?;
             }
         }
@@ -275,7 +275,7 @@ fn bump(version: String) -> Result<()> {
         if let Some(hooks) = &hooks {
             if let Some(post_func) = hooks.get("post_func") {
                 post_func
-                    .call(())
+                    .call::<_, ()>(())
                     .map_err(|source| Error::LuaPostFuncFailed { source })?;
             }
         }