[MISC] Disable cached builds

[dragomirp]

Cached psycopg 3 whl for amd64 fails when imported with:

ImportError: no pq wrapper available.
Attempts made:
- couldn't import psycopg 'c' implementation: /var/lib/juju/agents/unit-pgbouncer-k8s-2/charm/venv/psycopg_c/pq.cpython-310-x86_64-linux-gnu.so: undefined symbol: PQchangePassword

E.g. https://github.com/canonical/pgbouncer-k8s-operator/actions/runs/11273320303/job/31350375338?pr=441

Disabling the cached builds to fix builds.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.79%. Comparing base (260d9e5) to head (391d616).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #442   +/-   ##
=======================================
  Coverage   71.79%   71.79%           
=======================================
  Files           8        8           
  Lines        1280     1280           
  Branches      243      243           
=======================================
  Hits          919      919           
  Misses        276      276           
  Partials       85       85           

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[taurus-forever]

CC: @carlcsaposs-canonical JFYI (re: charmcraftcache).