fix: font size flag change to boolean (#9290)

## About the changes
Fix for `uiGlobalFontSize` flag being returned as an object, which is truthy.

Author: Tymek

frontend/src/interfaces/uiConfig.ts

@@ -93,7 +93,7 @@ export type UiFlags = {
     granularAdminPermissions?: boolean;
     frontendHeaderRedesign?: boolean;
     dataUsageMultiMonthView?: boolean;
-    uiGlobalFontSize?: Variant;
+    uiGlobalFontSize?: boolean;
 };
 
 export interface IVersionInfo {

src/lib/types/experimental.ts

@@ -310,17 +310,10 @@ const flags: IFlags = {
         process.env.UNLEASH_EXPERIMENTAL_DATA_USAGE_MULTI_MONTH_VIEW,
         false,
     ),
-    uiGlobalFontSize: {
-        name: 'uiGlobalFontSize',
-        enabled: parseEnvVarBoolean(
-            process.env.EXPERIMENTAL_UI_GLOBAL_FONT_SIZE_NAME,
-            false,
-        ),
-        payload: {
-            type: PayloadType.JSON,
-            value: '14',
-        },
-    },
+    uiGlobalFontSize: parseEnvVarBoolean(
+        process.env.EXPERIMENTAL_UI_GLOBAL_FONT_SIZE_NAME,
+        false,
+    ),
 };
 
 export const defaultExperimentalOptions: IExperimentalOptions = {