feat: replace %{?systemd_requires} with %{?systemd_ordering}

As said [in the documentation](https://docs.fedoraproject.org/en-US/packaging-guidelines/Scriptlets/#_dependencies_on_the_systemd_package):

> If the package wants to use systemd tools if they are available, but does not
want to declare a dependency, then the `%{?systemd_ordering}` macro MAY be used
as a weaker form of %{?systemd_requires} that only declares an ordering during
an RPM transaction.

See 2424b6bd71
and https://pagure.io/packaging-committee/issue/644 for more information.

And also use `--setopt=install_weak_deps=False` to avoid installing a lot of
useless dependencies.

packaging/rpm/Dockerfile

@@ -5,7 +5,7 @@ WORKDIR /go/src/app
 RUN make miniflux
 
 FROM rockylinux:9
-RUN dnf install -y rpm-build systemd
+RUN dnf install --setopt=install_weak_deps=False -y rpm-build systemd-rpm-macros
 RUN mkdir -p /root/rpmbuild/{BUILD,RPMS,SOURCES,SPECS,SRPMS}
 RUN echo "%_topdir /root/rpmbuild" >> .rpmmacros
 COPY --from=build /go/src/app/miniflux /root/rpmbuild/SOURCES/miniflux

packaging/rpm/miniflux.spec

@@ -16,8 +16,7 @@ BuildRoot: %{_topdir}/BUILD/%{name}-%{version}-%{release}
 BuildArch: x86_64
 Requires(pre): shadow-utils
 
-%{?systemd_requires}
-BuildRequires: systemd
+%{?systemd_ordering}
 
 AutoReqProv: no