[CI] Pin the wheel-test torch to a shipped PG build

[he-yufeng]

Description

Fixes #4439.

The wheel test legs of CI are red on every PR right now. scripts/test_installation.sh installs torch unpinned, so PyPI's latest (2.14.1) lands in the test venv, while the wheel only ships PG builds for EP_TORCH_VERSIONS (currently up to 2.14.0). mooncake.pg then looks for mooncake.pg_2_14_1, and all six test_pg_* modules fail at import.

The wheel is already installed a few lines earlier in the same script, so it now enumerates the mooncake.pg_* modules the wheel ships and installs the newest matching torch. Wheels without PG builds (non-cuda variants, or any detection failure) keep the previous unpinned behavior, so the change cannot make a green run worse.

Module

• CI/CD

Type of Change

• Bug fix

How Has This Been Tested?

Test commands:

bash -n scripts/test_installation.sh
# detection snippet run against a stub mooncake package with five fake
# pg_*.so builds (2.11.0 .. 2.14.0), against one with no PG modules, and
# against an environment where import mooncake fails outright

Test results:

• stub with five PG builds: resolves torch==2.14.0, the newest shipped variant
• stub with no PG modules: empty result, falls back to unpinned pip install torch numpy
• import failure: || true keeps set -e intact, same fallback
• the end-to-end validation is this PR's own test-wheel-ubuntu legs, which should go green again

Checklist

• I have performed a self-review of my own code
• I have run pre-commit on the files changed in this PR and all hooks pass (shell script, verified with bash -n; no pre-commit hook covers it)
• I have updated the documentation (not applicable, no behavior change for users)
• I have added tests to prove my changes are effective (the CI pipeline itself is the test: this leg is red on every open PR today)

AI Assistance Disclosure

• AI tools were used (specify below)

Kimi Code drafted the change; verification steps above were actually run as described, and the submitter has reviewed every changed line.

[he-yufeng]

Status update: the end-to-end validation the description was waiting for is in. Both test-wheel-ubuntu legs pass on this PR (py312 in 20m58s, py310 in 6m22s), while the same job fails on every other open PR with ImportError: Mooncake PG was not built against torch==2.14.1 (example: job 110676867503 on #4450).

Since this unblocks CI for the whole open queue, a review when someone has a moment would help. @Aionw you merged most of the recent CI fixes, maybe you have context on this one.