[Fleet] fix validate package policy error (elastic#208528)

## Summary

Closes elastic#208519

To verify:
- Add Network Packet Capture integration
- verify that there is no UI error when adding the package policy

<img width="1418" alt="image"
src="https://github.com/user-attachments/assets/2806f717-995a-4c7a-9532-08be30f0cd10"
/>

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

x-pack/platform/plugins/shared/fleet/common/services/validate_package_policy.test.ts

@@ -1243,6 +1243,25 @@ describe('Fleet - validatePackagePolicyConfig', () => {
 
       expect(res).toEqual(['myvariable is required']);
     });
+
+    it('should accept integer', () => {
+      const res = validatePackagePolicyConfig(
+        {
+          type: 'text',
+          value: [1],
+        },
+        {
+          name: 'myvariable',
+          type: 'text',
+          multi: true,
+          required: true,
+        },
+        'myvariable',
+        load
+      );
+
+      expect(res).toBeNull();
+    });
   });
 
   describe('Integer', () => {

x-pack/platform/plugins/shared/fleet/common/services/validate_package_policy.ts

@@ -370,7 +370,8 @@ export const validatePackagePolicyConfig = (
     }
     if (varDef.required && Array.isArray(parsedValue)) {
       const hasEmptyString =
-        varDef.type === 'text' && parsedValue.some((item) => item.trim() === '');
+        varDef.type === 'text' &&
+        parsedValue.some((item) => typeof item === 'string' && item.trim() === '');
 
       if (hasEmptyString || parsedValue.length === 0) {
         errors.push(