Collation lost when changing type from varchar to text

[Verdurakh]

Bug description

When changing a type of a column from varchar to text the previously set collation seems to be lost.

The migration adds a Alter Column statement specifying the same collation for both old and new.

My expected sql code would have been something like

ALTER TABLE address ALTER COLUMN tag TYPE text COLLATE case_insensitive;
which if done manually works and keeps the collation but this is not what is happening in the migration.

orginial Entity Configuration
	builder.Property(address => address.Tag).HasMaxLength(50);            
When removing the HasMaxLength(5) the below migration is created.

public class AddressEntity 
{
	
	public required string? Tag { get; set; }
}



migrationBuilder.AlterColumn<string>(
                name: "tag",
                table: "address",
                type: "text",
                nullable: true,
                collation: "case_insensitive",
                oldClrType: typeof(string),
                oldType: "character varying(50)",
                oldMaxLength: 50,
                oldNullable: true,
                oldCollation: "case_insensitive");

After this the collation for this column is null

[Verdurakh]

Note that if I set the oldCollation = null it works as expected

[Verdurakh]

seems to be from here
https://github.com/npgsql/efcore.pg/blob/main/src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs
Line 459

        if (type != oldType || newCollation != oldCollation)
        {
            builder
                .Append(alterBase)
                .Append("TYPE ")
                .Append(type);

            if (newCollation != oldCollation)
            {
                builder.Append(" COLLATE ").Append(DelimitIdentifier(newCollation ?? "default"));
            }

            builder.AppendLine(";");
        }

[roji]

Thanks @Verdurakh, have pushed a fix in #3476 and will backport to 9.0.4.