copr-builders: do not enforce digest verification on the host

It is standard practice to use Mock's bootstrap image feature now, so
the vast majority of builds are not affected by the host's RPM
configuration.

However, some workarounds remain—such as for epel-7-ppc64le (where an
architecture-specific UBI7 image is unavailable).  In these cases, we
still need to install the bootstrap chroot using the older method
(`dnf install yum` via the host's DNF/RPM).  This process would fail for
target distributions that were using SIGMD5 digests if verification were
enforced:

| Error: Transaction test error:
|   package libgcc-4.8.5-44.el7.ppc64le does not verify: no digest
|   package tzdata-2024a-1.el7.noarch does not verify: no digest
|   ...

Regardless of this change, we still perform gpgcheck=1 for target
buildroots.  However, these checks are handled by the RPM/DNF stacks
inside the bootstrap environments.  Therefore, this change specifically
affects bootstrap chroot installations (primarily for older targets) on
builder hosts running RPM v6 (Fedora 43+).

See also: infra/ansible#3122

roles/copr/backend/files/provision/provision_builder_tasks.yml

@@ -231,6 +231,15 @@
     - from: epel-9-x86_64.cfg
       to: rhel+epel-9-x86_64.cfg
 
+- name: "allow installing RPMs with (obsolete) MD5/SHA1 digests"
+  ansible.builtin.copy:
+    content: |
+      %_pkgverify_flags 0
+    dest: /etc/rpm/macros.verify
+    owner: root
+    group: root
+    mode: "0644"
+
 - name: run /bin/copr-update-builder from copr-builder package
   ansible.builtin.shell: /usr/bin/copr-update-builder