fix(PageHeader): use display block insteaf of flex when FF off (#5402)

* fix(PageHeader): use display block insteaf of flex when FF off

* Create cold-bags-move.md

Author: francinelucca

.changeset/cold-bags-move.md

@@ -0,0 +1,5 @@
+---
+"@primer/react": patch
+---
+
+fix(PageHeader): use display block insteaf of flex when FF off

packages/react/src/PageHeader/PageHeader.tsx

@@ -546,7 +546,7 @@ const Title: React.FC<React.PropsWithChildren<TitleProps>> = ({
                 display: 'flex',
                 order: TITLE_AREA_REGION_ORDER.Title,
                 ...getBreakpointDeclarations(hidden, 'display', value => {
-                  return value ? 'none' : 'flex'
+                  return value ? 'none' : 'block'
                 }),
                 fontSize: 'inherit',
                 fontWeight: 'inherit',