Correct syntax for mv comments

[jeremyyeo]

resolves #837

Problem

Comments on mv's were using the wrong syntax on redshift.

Solution

Modified the redshift__alter_relation_comment macro so that it has the right syntax.

$ dbt run
...
05:38:04  Using redshift connection "model.my_dbt_project.my_mv"
05:38:04  On model.my_dbt_project.my_mv: /* {"app": "dbt", "dbt_version": "1.9.0a1", "profile_name": "rs", "target_name": "dev", "node_id": "model.my_dbt_project.my_mv"} */

    comment on view "dev"."public"."my_mv" is $dbt_comment_literal_block$Lorem ipsum$dbt_comment_literal_block$;
05:38:05  SQL status: SUCCESS in 0.405 seconds
05:38:05  On model.my_dbt_project.my_mv: COMMIT
...

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-redshift contributing guide.

[jeremyyeo]

@dbt-labs/adapters I don't really know what I'm doing with the test here - just cribbed what @colin-rogers-dbt had on dbt-labs/dbt-postgres#11 😁