hash/crc32: fix incorrect checksums with avx512+race

[klauspost]

CRC value loaded from incorrect register, which happened
to line up with actual register on default compile.
Therefore failures would only show up with -race.

Add regression test with longer payloads.

Fix regression from CL 689435.

Fixes #74767.

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from t hepudds:

Patch Set 4: Commit-Queue+1

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Message from Go LUCI:

Patch Set 4:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2025-07-28T15:29:33Z","revision":"6b1b4b19f1ac45cf9206b608bd28546243d0c5b5"}

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Message from Keith Randall:

Patch Set 4: Auto-Submit+1 Code-Review+2

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Message from Keith Randall:

Patch Set 4: Code-Review+1

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Message from David Chase:

Patch Set 4: Code-Review+2 Commit-Queue+1

(1 comment)

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This PR is being closed because golang.org/cl/690855 has been merged.