Add PG17 to build matrix for Citus upgrade tests

[onurctirtir]

As of citusdata/the-process#175, our images already support PG17 for Citus upgrade tests, so let's also test it in our CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.78%. Comparing base (b7a5f69) to head (1185b1b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8423      +/-   ##
==========================================
- Coverage   88.79%   88.78%   -0.01%     
==========================================
  Files         287      287              
  Lines       63236    63237       +1     
  Branches     7928     7928              
==========================================
- Hits        56150    56148       -2     
- Misses       4754     4756       +2     
- Partials     2332     2333       +1     

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