fix(test): make instrumented migrator tests return Unit

`@Test fun x() = runBlocking { ... }` whose block ends in `.apply { }`
returns the DB (non-Unit), so JUnit4 rejects the whole class at runtime
with InvalidTestClassError ("method should be void") — which compiles
fine locally but fails every E2E job on the emulator. Use
`runBlocking<Unit>` (the existing DatabaseEncryptionTest idiom) so the
methods are void while keeping the expression body ktlint expects.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/androidTest/kotlin/org/libremail/data/local/AccountDataMigratorTest.kt

@@ -92,7 +92,7 @@ class AccountDataMigratorTest {
         Room.databaseBuilder(context, AccountDatabase::class.java, accountsName).build()
 
     @Test
-    fun movesEveryAccountTableOutOfAPlaintextCache() = runBlocking {
+    fun movesEveryAccountTableOutOfAPlaintextCache() = runBlocking<Unit> {
         seedVersion14Cache()
 
         AccountDataMigrator.copyAccountTables(cacheFile, cachePassphrase = "", accountsFile = accountsFile)
@@ -121,7 +121,7 @@ class AccountDataMigratorTest {
     }
 
     @Test
-    fun movesAccountsOutOfAnEncryptedCache() = runBlocking {
+    fun movesAccountsOutOfAnEncryptedCache() = runBlocking<Unit> {
         seedVersion14Cache()
         // Turn the cache into the SQLCipher form an app-lock + encrypted-cache user has on disk.
         DatabaseEncryption.ensureEncrypted(cacheFile, passphrase)
@@ -141,7 +141,7 @@ class AccountDataMigratorTest {
     }
 
     @Test
-    fun reRunningTheCopyIsIdempotentAndKeepsLaterEdits() = runBlocking {
+    fun reRunningTheCopyIsIdempotentAndKeepsLaterEdits() = runBlocking<Unit> {
         seedVersion14Cache()
         AccountDataMigrator.copyAccountTables(cacheFile, cachePassphrase = "", accountsFile = accountsFile)
 
@@ -167,7 +167,7 @@ class AccountDataMigratorTest {
     }
 
     @Test
-    fun accountsAndCredentialsSurviveACacheWipe() = runBlocking {
+    fun accountsAndCredentialsSurviveACacheWipe() = runBlocking<Unit> {
         seedVersion14Cache()
         AccountDataMigrator.copyAccountTables(cacheFile, cachePassphrase = "", accountsFile = accountsFile)
 

app/src/androidTest/kotlin/org/libremail/data/local/AccountDatabaseTest.kt

@@ -49,7 +49,7 @@ class AccountDatabaseTest {
     )
 
     @Test
-    fun credentialRoundTripsAndIsIndependentOfTheAccountRow() = runBlocking {
+    fun credentialRoundTripsAndIsIndependentOfTheAccountRow() = runBlocking<Unit> {
         db.accountDao().upsert(account())
         db.credentialDao().upsert(CredentialEntity("acct", "sealed-secret"))
 
@@ -57,7 +57,7 @@ class AccountDatabaseTest {
     }
 
     @Test
-    fun accountSettingsRoundTripAndCascadeWithTheirAccount() = runBlocking {
+    fun accountSettingsRoundTripAndCascadeWithTheirAccount() = runBlocking<Unit> {
         db.accountDao().upsert(account())
         db.accountSettingsDao().upsert(
             AccountSettingsEntity("acct", signature = "Hi", signatureEnabled = false, notificationsEnabled = false),
@@ -70,7 +70,7 @@ class AccountDatabaseTest {
     }
 
     @Test
-    fun signaturesCascadeWithTheirAccount() = runBlocking {
+    fun signaturesCascadeWithTheirAccount() = runBlocking<Unit> {
         db.accountDao().upsert(account())
         db.signatureDao().upsert(SignatureEntity("sig-1", "acct", "Work", "<p>Regards</p>", isDefault = true))
         assertEquals(1, db.signatureDao().observeForAccount("acct").first().size)