git-series: add --locked flag to cargo install

[chenrui333]

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

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Relates to #46025

[samford]

The CI build is failing here because the lock file in git-series v0.9.1 (latest) uses an old version of git2, which uses an old version of libgit2-sys, which uses an old version of openssl-sys that has a build error.

The v0.9.1 release is nearly three years old now, so it's no surprise that the build fails. It looks like the creator started working on it again in October and added a number of commits, one of which bumps the git2 version and fixes this issue.

I would say it's best not to add the --locked flag in the current state and to wait for a new release. It's possible to build from master but, because of the recent changes, it may not be fully ready for use.

[chenrui333]

@samford Sounds good, let's do it in the new release!