Cannot Connect to 6.x Image in GitHub Workflow

[theory]

I have been adding tests to Sqitch, including its support for the Exasol engine, here. It's working well for Versions 7.0 and 7.1, but not for 6.x. I am using the 7.x ODBC driver and EXAplus clients. The ODBC connection failure is:

[EXASOL][EXASolution driver]Error in SSL_connect. SSL error code: 5 = SSL_ERROR_SYSCALL    (SQL-HY000) [state was HY000 now 01002]
[EXASOL][EXASolution driver]Exasol was not connected. (SQL-01002)

The error is the same with SSLCertificate=SSL_VERIFY_NONE and without. Note that it works fine (with SSLCertificate=SSL_VERIFY_NONE) connecting to Exasol 7 (example).

I also tried installing the 6.2 ODBC driver, and that returns a different error:

[EXASOL][EXASolution driver]Error in socket read. (SQL-HY000)
[EXASOL][EXASolution driver]Error code was 0 (SQL-HY000) [state was HY000 now 08S01]
[EXASOL][EXASolution driver]Error receiving message from Exasol. Socket failure. (SQL-08S01)

Which makes it seem like it's not running, but the "Initialize Containers" step clearly shows it starting up just fine. Any idea what might be preventing connections to 6.x in GitHub Actions?