pijul: Add --locked flag to cargo install

[samford]

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• Have you checked that there aren't other open pull requests for the same formula update/change?
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As discussed in #44041 (and #46025), adding the --locked flag to cargo install will fix the build for Pijul v0.12.0 while we wait for them to add tar.gz files on their website for newer releases (open issue here: https://nest.pijul.com/pijul_org/pijul/discussions/425).

[fxcoudert]

Many thanks @samford for the pull requests! You rock