test: Make test test-26-examples-build support multi arch

Signed-off-by: Xiaofeng Wang <henrywangxf@me.com>

Author: henrywang

tmt/tests/examples/bootc-uki/Containerfile.stage2

@@ -25,11 +25,13 @@ RUN --mount=type=secret,id=key \
         --measure \
         --json pretty \
         --output "/boot/$kver.efi"
+    # To support multi arch
+    systemd_boot_file=$(ls /usr/lib/systemd/boot/efi/*.efi | xargs -n 1 basename)
     sbsign \
         --key "/run/secrets/key" \
         --cert "/run/secrets/cert" \
-        "/usr/lib/systemd/boot/efi/systemd-bootx64.efi" \
-        --output "/boot/systemd-bootx64.efi"
+        "/usr/lib/systemd/boot/efi/${systemd_boot_file}" \
+        --output "/boot/${systemd_boot_file}"
 EOF
 
 FROM base as final