fix(sentry-admin): Run the container once for --help

[oioki]

rename_sentry_bin_in_help_output already receives the help output as $1, but it ran the container a second time with its own arguments, so the whole help text was passed as the command. The old bash entrypoint echoed that argument in its exec error, so the help still showed up by accident. The sentry image's new Python entrypoint (getsentry/sentry#125892) doesn't, so ./sentry-admin.sh --help on :nightly prints only a traceback and test_sentry_admin fails. This also makes --help start one container instead of two.

Unblocks #4536, and self-hosted master's scheduled tests now that :nightly includes #125892.

[oioki]

Folded into #4536.

[github-actions]

Coverage Results 📊

✅ 17 passed | ⏭️ 5 skipped | Total: 22 | Pass Rate: 77.27% | Execution Time: 8m 0s

📊 Comparison with Base Branch

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

✨ Test counts unchanged from base.

All tests are passing successfully.

✅ Patch coverage is 100.00% (no changed executable lines found; target 50%).
Project statement coverage is 82.44% (unchanged from base (85ef848) to head (25748a6)).

Coverage diff

@@            Coverage Diff             @@
##        master     #4537       +/-##
==========================================
  Coverage    82.44%    82.44%        —%
==========================================
  Files            5         5         —
  Tracked lines       336       336         —
  Branches         0         0         —
==========================================
  Hits           277       277         —
  Misses          59        59         —
  Partials         0         0         —

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