test(db): drop a leftover test database before recreating it

A server handed in through JELLYFIN_TEST_POSTGRES outlives the run, so a second
run finds the databases the first one created. Also name the failures in
Jellyfin.Database.Tests.PostgreSQL the CI step steps around.

tests/Jellyfin.Server.Tests/Migrations/PostgreSqlTestServer.cs

@@ -65,6 +65,12 @@ public sealed class PostgreSqlTestServer : IAsyncDisposable
     public async Task<string> CreateDatabaseAsync(string name, CancellationToken cancellationToken)
     {
         await using var adminDataSource = new NpgsqlDataSourceBuilder(ConnectionString).Build();
+
+        // A server handed in through the environment outlives the run, so a second run finds the
+        // databases the first one left behind.
+        await using var drop = adminDataSource.CreateCommand($"DROP DATABASE IF EXISTS {name}");
+        await drop.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);
+
         await using var command = adminDataSource.CreateCommand($"CREATE DATABASE {name}");
         await command.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);