Fix the semicolon semantics for indexes while respecting other bug fix.

[VersusFacit]

resolves #85
docs dbt-labs/docs.getdbt.com/#

Problem

Reprex now added as test and replicated locally!

@mikealfare shared this lovely context, re the comment linked in the issue ticket (here). We removed a ; at the postgres__get_create_index_sql macro to solve a different problem sending up empty queries when getting this merged:

We do not appear to be updating cache for MV functionality like drops, renames, adds which is causing catalog mismatch errors in runs especially between MV's that are dependent on each other

This however was incomplete as a solution because we needed to only leave off the last ; from various index create/alter statements.

Solution

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

[mikealfare]

This needs a changelog, otherwise it looks good.

[jtcohen6]

FYI @VersusFacit - We need to backport this fix for inclusion in v1.7.x + v1.8.x, because this was a regression introduced in v1.7.14. I don't believe we have the backport workflow set up in this repo yet, so we either need to backport manually or set up that workflow.