feat(toxgen): Forward args from generate-test-files script

[sentrivana]

• Forward any args provided to generate-test-files.sh to toxgen, so you can do e.g. ./scripts/generate-test-files.sh --only django and only django test matrix entries will be updated.
• Rename the two existing options from --skip-version-update and --only-update to --skip and --only, respectively, to simplify.
• Print an info message if either is set.

[github-actions]

Codecov Results 📊

✅ 94982 passed | ⏭️ 6343 skipped | Total: 101325 | Pass Rate: 93.74% | Execution Time: 340m 32s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2504 uncovered lines.
✅ Project coverage is 89.92%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.89%    89.92%    +0.03%
==========================================
  Files          193       193         —
  Lines        24832     24832         —
  Branches      8912      8912         —
==========================================
+ Hits         22321     22328        +7
- Misses        2511      2504        -7
- Partials      1415      1415         —

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