[Navigation] Fix secondary navigation spacing when no icon is present

UNRELEASED.md

@@ -7,6 +7,7 @@
 ### Bug fixes
 
 - Fixed right padding styling issue with the `Tag` component and remove right padding on a removable `Tag` ([#2860](https://github.com/Shopify/polaris-react/pull/2860)).
+- Fixed secondary navigation spacing when no icon is present ([#2874](https://github.com/Shopify/polaris-react/pull/2874)).
 
 ### Documentation
 

src/components/Navigation/Navigation.scss

@@ -378,6 +378,10 @@ $secondary-item-font-size: rem(15px);
   }
 }
 
+.SecondaryNavigation-noIcon {
+  margin-left: spacing();
+}
+
 // Section styles
 .Section {
   @include unstyled-list;

src/components/Navigation/components/Item/Item.tsx

@@ -236,8 +236,13 @@ export function Item({
       ({url: firstUrl}, {url: secondUrl}) => secondUrl.length - firstUrl.length,
     )[0];
 
+    const SecondaryNavigationClassName = classNames(
+      styles.SecondaryNavigation,
+      !icon && styles['SecondaryNavigation-noIcon'],
+    );
+
     secondaryNavigationMarkup = (
-      <div className={styles.SecondaryNavigation}>
+      <div className={SecondaryNavigationClassName}>
         <Secondary expanded={showExpanded}>
           {subNavigationItems.map((item) => {
             const {label, ...rest} = item;