Update micro plain/monochrome Button text to small

This fix improves text size alignment on the FilterBar component. The "Clear all" button is now the same size as the other buttons in the FilterBar.

.changeset/plenty-shoes-remain.md

@@ -0,0 +1,5 @@
+---
+'@shopify/polaris': minor
+---
+
+Updated plain/monochrome Button text size to bodySm for micro

polaris-react/src/components/Button/Button.tsx

@@ -176,10 +176,15 @@ export function Button({
     textFontWeight = mdUp ? 'medium' : 'semibold';
   }
 
+  let textVariant: TextProps['variant'] = 'bodySm';
+  if (size === 'large' || (hasPlainText && size !== 'micro')) {
+    textVariant = 'bodyMd';
+  }
+
   const childMarkup = children ? (
     <Text
       as="span"
-      variant={size === 'large' || hasPlainText ? 'bodyMd' : 'bodySm'}
+      variant={textVariant}
       fontWeight={textFontWeight}
       // Fixes Safari bug that doesn't re-render button text to correct color
       key={disabled ? 'text-disabled' : 'text'}