fix(L2): update ContentPin tests for 6-digit PIN validation

[Copilot]

SetContentPin regex changed from ^\d{4}$ to ^\d{6}$, making all existing L2 tests that set "1234" invalid. Added coverage for the new rejection behavior.

Changes

• Updated existing pin values — "1234" → "123456" in all setter call sites and assertions across getMigrationStatecase, onContentPinChangedEvent, and SetAndGetMethodsUsingComRpcConnectionSuccessCase

• SetContentPin_InvalidFourDigitPinReturnsError — asserts the previously-valid 4-digit PIN now returns Core::ERROR_INVALID_PARAMETER and fires no change notification

• SetContentPin_InvalidFormatPinReturnsError — asserts non-numeric ("abcdef"), 5-digit ("12345"), and 7-digit ("1234567") inputs all return Core::ERROR_INVALID_PARAMETER with no notification side-effect

// Before (accepted)
status = m_usersettingsplugin->SetContentPin("1234");
EXPECT_EQ(status, Core::ERROR_NONE);

// After (rejected)
status = m_usersettingsplugin->SetContentPin("1234");
EXPECT_EQ(status, Core::ERROR_INVALID_PARAMETER);

// Valid 6-digit form
status = m_usersettingsplugin->SetContentPin("123456");
EXPECT_EQ(status, Core::ERROR_NONE);