unbreak gptq int4 test and add to CI

[vkuzo]

Summary:

1. makes the gptq test with int4 pass locally
2. add it to the 1xh100 CI job (which has mslk)

Test Plan:

pytest test/prototype/gptq/test_gptqv2.py -s -k "naive and int4"

[vkuzo]

Stack from ghstack (oldest at bottom):

• gptq: more obvious inner loop var names #4227
• gptq: more obvious group var names #4226
• gptq: more obvious block var names #4225
• gptq: rename W to W_t #4224
• -> unbreak gptq int4 test and add to CI #4223

[pytorch-bot]

🔗 Helpful Links

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As of commit 916714b with merge base c49a60e ():
💚 Looks good so far! There are no failures yet. 💚

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