Existing tables not found or updated correctly if incoming schema name isn't lower cased

[tombriggsallego]

Describe the bug
If the incoming schema isn't all lower case (e.g. "MySchema") the code will conclude the tables don't exist and try to recreate them.

To Reproduce
Steps to reproduce the behavior:

1. Create a schema in MySQL with a mixed-case name (e.g. "MySchema")
2. Create a table in said schema and put some data in it
3. Set up a pipeline from MySQL to Postgres and run it. Let target-postgres create the destination schema. This will result in a schema in PG named "myschema"
4. Add some new data to the table in MySQL.
5. Re-run the pipeline. target-postgres will log a message saying the table doesn't exist and try to recreate it.

Note that the CREATE TABLE succeeds without error because it includes an IF NOT EXISTS clause. However, if you add a column to your source table the pipeline will fail - because the code thinks the table doesn't exist it tries to create it rather than update the schema.

Expected behavior
The existing table should be recognized, no log message should be generated, and any schema updates should be applied.

Your environment

• Version of target: git latest
• Version of python 3.8
• Meltano latest