ci: use dnf builddep to install make-rpm build dependencies

greenboot-rs.spec has an unconditional BuildRequires: systemd-rpm-macros,
but the make-rpm job's dnf install step never installs it, only
git/make/rpm-build/rust-toolset. rpmbuild then fails dependency
resolution before it ever gets to building anything:

  error: Failed build dependencies:
      systemd-rpm-macros is needed by greenboot-rs-0.16.3-0.el9.x86_64

Rather than hardcode systemd-rpm-macros alongside rust-toolset (which
would just be one more package to keep in sync with the spec by hand),
use 'dnf builddep' against greenboot-rs.spec directly so the job always
installs whatever the spec's BuildRequires actually resolve to on this
container, including the rust-toolset/cargo-rpm-macros conditional
branch, with no separate list to maintain.

Verified against the exact quay.io/centos/centos:stream9 image the job
uses: 'dnf install -y git make rpm-build dnf-plugins-core' followed by
'dnf builddep -y greenboot-rs.spec' correctly resolves rust-toolset and
systemd-rpm-macros, and 'make rpm' completes and produces all four
expected RPMs.

Also checked this doesn't regress the Fedora build path: 'dnf builddep'
alone only sees the spec's static BuildRequires, not the per-crate
rust-*-devel packages that %generate_buildrequires/
%cargo_generate_buildrequires enumerate dynamically during %prep on
Fedora. That's fine here because this CI job only ever runs in the
CentOS Stream 9 container above; the Fedora path is handled entirely
separately by the Makefile's own Fedora-conditional dnf install of
GREENBOOT_RUST_DEPENDENCIES, which this change doesn't touch.

Assisted-by: OpenCode (Claude Sonnet 5)

Author: miabbott

.github/workflows/comment-ci.yaml

@@ -59,7 +59,8 @@ jobs:
 
       - name: Build RPMs
         run: |
-          dnf install -y git make rpm-build rust-toolset
+          dnf install -y git make rpm-build dnf-plugins-core
+          dnf builddep -y greenboot-rs.spec
           make rpm
 
       - name: Verify RPMs were created

.github/workflows/greenboot-ci.yaml

@@ -59,7 +59,8 @@ jobs:
 
       - name: Build RPMs
         run: |
-          dnf install -y git make rpm-build rust-toolset
+          dnf install -y git make rpm-build dnf-plugins-core
+          dnf builddep -y greenboot-rs.spec
           git config --global --add safe.directory /__w/greenboot-rs/greenboot-rs
           make rpm