Try adding python3-venv to an Aptfile

[bickelj]

Try adding python3-venv to an Aptfile

The goal is to restore the Digital Ocean (DO) deployment pipeline
while keeping the existing lint command that now includes sqlfluff
calls. The assumption is that an Ubuntu Jammy image is being built and
that when an Aptfile is present, DO will use it before or during a build.

The specific error we're getting at deploy time is this:

postinstall

[ ! -d "venv" ] && python3 -m venv venv; ./venv/bin/pip install -r sqlfluff/requirements.txt
The virtual environment was not created successfully because ensurepip is not
available. On Debian/Ubuntu systems, you need to install the python3-venv
package...

See https://docs.digitalocean.com/products/app-platform/reference/buildpacks/aptfile/

Hat tip to Daniel Schultz for finding that documentation.

Issue #1410

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.30%. Comparing base (26f8d6f) to head (04fff54).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1416   +/-   ##
=======================================
  Coverage   87.30%   87.30%           
=======================================
  Files         209      209           
  Lines        2876     2876           
  Branches      400      408    +8     
=======================================
  Hits         2511     2511           
+ Misses        365      336   -29     
- Partials        0       29   +29     

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