build_speed: Update chrome_junit_sig benchmark anchor

The previous anchor text contained annotations that would inadvertently
be applied to the new interface method instead of the original test
method, causing static analysis failures.

This change updates the anchor to a more stable field declaration to fix
the benchmark build.

[email protected]

Bug: 465514549
Change-Id: I4a4ab04a4d2a66cdac86c78936283735789e6fd7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7243430
Commit-Queue: Henrique Nakashima <[email protected]>
Reviewed-by: Henrique Nakashima <[email protected]>
Auto-Submit: Peter Wen <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1556343}
NOKEYCHECK=True
GitOrigin-RevId: a97724cc61a6feb9fab36bca8cca153f5a619bfe
3 files changed