[SPARK-35388][INFRA] Allow the PR source branch to include slashes.

[ueshin]

What changes were proposed in this pull request?

This PR allows the PR source branch to include slashes.

Why are the changes needed?

There are PRs whose source branches include slashes, like issues/SPARK-35119/gha here or #32523.

Before the fix, the PR build fails in Sync the current branch with the latest in Apache Spark phase.
For example, at #32523, the source branch is issues/SPARK-35382/nested_higher_order_functions:

...
fatal: couldn't find remote ref nested_higher_order_functions
Error: Process completed with exit code 128.

(https://github.com/ueshin/apache-spark/runs/2569356241)

Does this PR introduce any user-facing change?

No, this is a dev-only change.

How was this patch tested?

This PR source branch includes slashes and #32525 doesn't.

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/42993/

[SparkQA]

Kubernetes integration test status failure
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/42993/

[SparkQA]

Test build #138472 has finished for PR 32524 at commit 3a8c5af.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[ueshin]

cc @HyukjinKwon @dongjoon-hyun

[HyukjinKwon]

Merged to master.