ci: optimize Prospector static analysis workflow

[ukanga]

Changes / Features implemented

• Optimized the Prospector static analysis workflow.
• Added APT package caching for the Prospector job.
• Moved the Prospector job APT package list into .github/apt-packages.txt so the cache key can be based on the package list.
• Removed the redundant Install linting tools step because prospector==1.18.0 and pylint==4.0.5 are already installed from requirements/dev.pip.

Steps taken to verify this change does what is intended

• Confirmed .github/workflows/ci.yml parses as valid YAML.
• Confirmed the updated APT install shell block passes shell syntax validation.
• Confirmed requirements/dev.pip includes:
  • prospector==1.18.0
  • pylint==4.0.5
• Ran Prospector locally:

DJANGOSETTINGSMODULE=onadata.settings.githubactionstest \
  .venv/bin/prospector -X -s veryhigh onadata


Result: Messages Found: 0

Side effects of implementing this change

• The Prospector CI job should spend less time downloading APT packages on cache hits.
• No expected change to the Prospector analysis behavior or command.

Before submitting this PR for review, please make sure you have:

• Included tests
• Updated documentation

Closes #3064

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