manibuilder/almalinux: Install `diffutils' for new `test_build.sh'

Change-Id: I6bb4d15761afc049cf1e7e7a2e84c13ae0eacc79
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/143
diff --git a/util/manibuilder/Dockerfile.almalinux b/util/manibuilder/Dockerfile.almalinux
index 8f3502d..e259955 100644
--- a/util/manibuilder/Dockerfile.almalinux
+++ b/util/manibuilder/Dockerfile.almalinux
@@ -14,6 +14,8 @@
 	{ dnf install -y libgpiod-devel || true; } && \
 	dnf clean -y all
 
+RUN dnf install -y diffutils && dnf clean -y all
+
 RUN mkdir -p -m 1777 /ccache
 
 ENV GIT_SSL_NO_VERIFY=1