feat(FeatureFlags): broaden feature flag type to accept undefined (#4554)

* feat(FeatureFlags): loosen feature flag type to accept undefined

* chore: add changeset

* Update .changeset/grumpy-coats-worry.md

---------

Co-authored-by: Josh Black <[email protected]>

Author: joshblack

.changeset/grumpy-coats-worry.md

@@ -0,0 +1,5 @@
+---
+'@primer/react': minor
+---
+
+Broaden feature flag type for experimental FeatureFlags to accept undefined

packages/react/src/FeatureFlags/FeatureFlagScope.ts

@@ -1,5 +1,5 @@
 export type FeatureFlags = {
-  [key: string]: boolean
+  [key: string]: boolean | undefined
 }
 
 export class FeatureFlagScope {
@@ -24,7 +24,10 @@ export class FeatureFlagScope {
   flags: Map<string, boolean>
 
   constructor(flags: FeatureFlags = {}) {
-    this.flags = new Map(Object.entries(flags))
+    this.flags = new Map()
+    for (const [key, value] of Object.entries(flags)) {
+      this.flags.set(key, value ?? false)
+    }
   }
 
   /**