The cross-repo CI testing on `release/5.10` doesn't work

[hjyamauchi]

Description

The "Please test with following PRs:" swift-ci command doesn't pick up the associated PR in the build.

Reproduction

For example, on #77277, the following command doesn't pick up the llvm-project PR, which includes an interface change in Clang, causes a build error:

Please test with following PRs:
https://github.com/swiftlang/llvm-project/pull/9478

@swift-ci please test

#77277 (comment)

Expected behavior

The "Please test with following PRs:" swift-ci command picks up the associated PR in the build.

Environment

The release/5.10 CI

Additional information

No response

[hjyamauchi]

Fix confirmed