`cargo install --path` ignores `Cargo.lock` unless `--locked` is given,
so every CI run re-resolved transitive deps fresh from crates.io. This
recently started failing on the `verify package can build` job: the
fresh resolution pulled in `rustix 0.37.28`, which uses `#[rustc_attrs]`
attributes that the current nightly compiler rejects with:

    error: attributes starting with `rustc` are reserved for use by the
           `rustc` compiler
      --> rustix-0.37.28/src/backend/linux_raw/io/errno.rs:28:25

`Cargo.lock` on `develop` already pins `rustix 1.1.2`, which builds
fine; the CI just wasn't honoring it.

Add `--locked` to every `cargo install --path cargo-pgrx` invocation
across the three workflow files (5 in tests.yml, 1 in runas.yml, 1 in
package-test.yaml) so CI uses the same resolution as `cargo build` and
becomes reproducible.