fix(FormLabel): Add missing class for col label sizing (react-bootstrap#5382)

Author: kyletsang

src/FormLabel.tsx

@@ -89,7 +89,9 @@ const FormLabel: FormLabel = React.forwardRef(
     bsPrefix = useBootstrapPrefix(bsPrefix, 'form-label');
 
     let columnClass = 'col-form-label';
-    if (typeof column === 'string') columnClass = `${columnClass}-${column}`;
+    if (typeof column === 'string')
+      columnClass = `${columnClass} ${columnClass}-${column}`;
+
     const classes = classNames(
       className,
       bsPrefix,

test/FormLabelSpec.js

@@ -77,13 +77,13 @@ describe('<FormLabel>', () => {
 
   it('should properly size itself when rendered as a Col', () => {
     mount(<FormLabel column="sm">Label</FormLabel>).assertSingle(
-      'label.col-form-label-sm',
+      'label.col-form-label.col-form-label-sm',
     );
     mount(<FormLabel column>Label</FormLabel>).assertSingle(
       'label.col-form-label',
     );
     mount(<FormLabel column="lg">Label</FormLabel>).assertSingle(
-      'label.col-form-label-lg',
+      'label.col-form-label.col-form-label-lg',
     );
     let labelComponent = mount(<FormLabel>Label</FormLabel>);
     labelComponent.assertNone('label.col-form-label');