fix(ui): prevent radio button ellipse distortion in RadioGroup

Fixed radio button circles becoming elliptical by preventing flex
shrink and grow on the button's ::before pseudo-element.

Signed-off-by: Johan Persson <johanopersson@gmail.com>

.changeset/ripe-crabs-care.md

@@ -0,0 +1,5 @@
+---
+'@backstage/ui': patch
+---
+
+Fixed RadioGroup radio button ellipse distortion by preventing flex shrink and grow.

packages/ui/src/components/RadioGroup/RadioGroup.module.css

@@ -54,6 +54,8 @@
       background: var(--bui-gray-1);
       border-radius: var(--bui-radius-full);
       transition: all 200ms;
+      flex-shrink: 0;
+      flex-grow: 0;
     }
 
     &[data-pressed]:before {