Minor url cache test enhancement (#4535)

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Add a check to make sure url cache's previous delta base doesn't change after refresh

---

#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

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- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [x] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

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* #<issue>

#### Test Plan

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- [ ] 💪 Manual
- [ ] ⚡ Unit test
- [ ] 💚 E2E

src/internal/m365/collection/drive/url_cache_test.go

@@ -184,6 +184,9 @@ func (suite *URLCacheIntegrationSuite) TestURLCacheBasic() {
 
 	// Validate that exactly 1 delta query was made by url cache
 	require.Equal(t, 1, uc.refreshCount)
+
+	// Validate that the prev delta base stays the same
+	require.Equal(t, du.URL, uc.prevDelta)
 }
 
 // ---------------------------------------------------------------------------