settings_ui: Fix stepper buttons to Inactive Opacity to 0.1 increment adjustments (#40477)

Closes #40279

Release Notes:

- Fix stepper buttons (+/-) to the Inactive Opacity setting for 0.1
increment adjustments on settings UI

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/workspace/src/workspace_settings.rs

@@ -4,11 +4,11 @@ use crate::DockPosition;
 use collections::HashMap;
 use serde::Deserialize;
 pub use settings::AutosaveSetting;
-use settings::Settings;
 pub use settings::{
     BottomDockLayout, PaneSplitDirectionHorizontal, PaneSplitDirectionVertical,
     RestoreOnStartupBehavior,
 };
+use settings::{InactiveOpacity, Settings};
 
 pub struct WorkspaceSettings {
     pub active_pane_modifiers: ActivePanelModifiers,
@@ -50,7 +50,7 @@ pub struct ActivePanelModifiers {
     ///
     /// Default: `1.0`
     // TODO: make this not an option, it is never None
-    pub inactive_opacity: Option<f32>,
+    pub inactive_opacity: Option<InactiveOpacity>,
 }
 
 #[derive(Deserialize)]