ci: use required-features instead for benches

[alxiong]

Description

I've been receiving CI failure (e.g. here) for the periodic-check.yml workflow, due to the build failure on some of our bench code.

As it turns out, whenever we want to use testing srs api, we use !#[features="test-srs"] in the code, which leads the compiler that by default doesn't build with this feature flag on to mistakenly assume there's no main() function in these bench code, thus erroring.

The proper way to do it, is simply add required-features in the Cargo.toml.

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (main)
• Linked to GitHub issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
• Updated relevant documentation in the code
• Added a relevant changelog entry to the Pending section in CHANGELOG.md
• Re-reviewed Files changed in the GitHub PR explorer

[tessico]

That's great!