Allow running `build-release.yml` against a branch

Currently, .github/workflows/build-release.yml takes a tag number:

https://github.com/python/release-tools/blob/9721c249ff1de736fcf180c4a806ce75372ebf2a/.github/workflows/build-release.yml#L35-L37

Which can be used as the input when triggering a run:

https://github.com/python/release-tools/actions/workflows/build-release.yml

It would be useful if we could also give a branch name, so for example we can trigger a run against upstream main or 3.14, so we can verify the latest state will build.

This will also help with PRs like https://github.com/python/release-tools/pull/284 where we specify which arguments to run against the Android test runner, and the test runner is in the upstream repo.

We'll need to take care of v prefix that is currently prepended in some places.

从 .github/workflows/build-release.yml 中第 35-37 行附近的输入定义开始，然后追踪该值的使用位置。支持分支名称和标签编号，同时保留现有的 v 前缀行为，并验证 workflow 是否既能基于 upstream main 或 3.14 构建，也能使用现有的标签输入。