ci: flaky tests

[skuruppu]

Expected Behavior

Test suite should pass against prod.

Actual Behavior

We see lots of different kinds of errors. Examples:

• "Transaction aborted. Database schema probably changed during transaction, retry may succeed." link
• Same as above except also with "InvalidArgument: 400 Column x is not present in table some_table [at 1:29]\nINSERT INTO some_table (id, x, y) VALUES (@a0, @A1, @a2)\n" link
• Migration tests seem to be passing but there is always an error "Transaction is already committed" link
• "FailedPrecondition: 400 Duplicate name in schema: noncol_idx_test_nopk" link

Steps to Reproduce the Problem

1. Create a PR and allow the CircleCI workflow to run.

[IlyaFaer]

The first error seems familiar, I think it's already fixed by this PR: googleapis/python-spanner#345
I'll keep an eye on it, but after #345 was merged, I didn't get single Aborted failure yet.

Column not present and Duplicate name most likely happening because someone executing the tests locally, in the same time the workflow do. I assume the PR #65 is not working fine, because we have a config tweaked for the concrete instance and database here:
https://github.com/cloudspannerecosystem/python-spanner-sqlalchemy/blob/092e6d874cb22daff350296e6c61b29aafc1f95a/setup.cfg#L29

Migrations - yeah, I also see this. There was an attempt to fix the similar error, but looks like it's not fixed yet:
#68

Okay, working on them.

[IlyaFaer]

These errors seem to be fixed, closing the issue, but will keep an eye.