Add CTS test for modify registered self-managed phone account.

Currently if the registered self-managed phone account updated to a call
provider phone account, the enable state will be directly copied to the
updated one so that malicious app can perform call spoofing attack
without any permission requirements. Fix this by disallowing change a
self-managed phone account to a managed phone account.

Bug: 246930197
Test: CtsTelecomTestCases:SelfManagedConnectionSreviceTest
Change-Id: I4951c295a9910be7956c3571db064ba99034ecae
Merged-In: I4951c295a9910be7956c3571db064ba99034ecae