Fix flaky Linux SQLite CI tests

src/Akka.Persistence.Sql.Tests.Common/Containers/MsSqliteContainer.cs

@@ -47,10 +47,11 @@ public async Task InitializeDbAsync()
         {
             GenerateDatabaseName();
 
+            _heldConnection ??= new List<SqliteConnection>();
             var conn = new SqliteConnection(ConnectionString);
             await conn.OpenAsync();
 
-            _heldConnection!.Add(conn);
+            _heldConnection.Add(conn);
         }
 
         public async Task DisposeAsync()

src/Akka.Persistence.Sql.Tests.Common/Containers/SqliteContainer.cs

@@ -46,10 +46,11 @@ public async Task InitializeDbAsync()
         {
             GenerateDatabaseName();
 
+            _heldConnection ??= new List<SQLiteConnection>();
             var conn = new SQLiteConnection(ConnectionString);
             await conn.OpenAsync();
 
-            _heldConnection!.Add(conn);
+            _heldConnection.Add(conn);
         }
 
         public async Task DisposeAsync()

src/Akka.Persistence.Sql.Tests/SqlDataOptionsEndToEndSpecBase.cs

@@ -45,6 +45,7 @@ private static Configuration.Config Config() =>  ConfigurationFactory.ParseStrin
         plugin = "akka.persistence.snapshot-store.sql"
     }
 }
+akka.test.single-expect-default = 10s
 """)
             .WithFallback(SqlPersistence.DefaultConfiguration);
 
@@ -89,7 +90,8 @@ public async Task InitializeAsync()
         public async Task DisposeAsync()
         {
             await Sys.Terminate();
-            await _fixture.DisposeAsync();
+            // Do NOT call _fixture.DisposeAsync() here - xUnit manages the collection fixture lifecycle.
+            // Disposing the shared fixture destroys in-memory databases for all other test classes in the collection.
         }
 
         /// <summary>

src/Akka.Persistence.Sql.Tests/SqlEndToEndSpecBase.cs

@@ -57,6 +57,7 @@ class = "Akka.Persistence.Sql.Snapshot.SqlSnapshotStore, Akka.Persistence.Sql"
         }
     }
 }
+akka.test.single-expect-default = 10s
 """;
 
         private const string GetAll = "getAll";

src/Akka.Persistence.Sql.Tests/Sqlite/SqliteEndToEndSpec.cs

@@ -10,7 +10,7 @@
 
 namespace Akka.Persistence.Sql.Tests.Sqlite
 {
-    [CollectionDefinition(nameof(SqlitePersistenceSpec), DisableParallelization = true)]
+    [Collection(nameof(SqlitePersistenceSpec))]
     public class SqliteEndToEndSpec: SqlEndToEndSpecBase<SqliteContainer>
     {
         public SqliteEndToEndSpec(ITestOutputHelper output, SqliteContainer fixture) : base(output, fixture) { }