Fix `ReadDatabase` when default collation set

[mostly-magic]

I discovered an issue with the ReadDatabase function when the collation is the default for the charset. While it makes the query to retrieve the default collation, it does not set the "default_character_set" and "default_collation" values on the ResourceData object.

Steps to Reproduce

1. Load the following resource

   resource "mysql_database" "test" {
       name = "test"
       default_character_set = "utf8"
       default_collation = "utf8_bin"
   }

2. Modify the database default collation

   ALTER DATABASE test COLLATE utf8_general_ci

3. Attempt to apply the first resource again

   resource "mysql_database" "test" {
       name = "test"
       default_character_set = "utf8"
       default_collation = "utf8_bin"
   }

Expected Behavior

Terraform should detect the modified collation and attempt to update the database

Actual Behavior

Terraform does not recognize the modification to collation and acts as though the database is still "utf8_bin"

[joestump]

Bug fix with a regression test. You get a FOSS 🍪today! Thanks so much!