Ensure cross test images have patch

For `armv7-linux-androideabi`, in

    GIX_TEST_IGNORE_ARCHIVES=1 cross test ...

as tested by running

    GIX_TEST_IGNORE_ARCHIVES=1 just cross-test-android

the `id::ancestors::pre_epoch` test failed with:

    /project/gix/tests/fixtures/make_pre_epoch_repo.sh: line 12: patch: command not found

This fixes it by making sure `patch` is installed in the container.

Author: EliahKagan

etc/docker/Dockerfile.test-cross

@@ -10,7 +10,7 @@ RUN apt-get update && \
     apt-key adv --keyserver keyserver.ubuntu.com \
         --recv-keys F911AB184317630C59970973E363C90F8F1B6217 && \
     apt-get update && \
-    apt-get install --no-install-recommends -y git jq && \
+    apt-get install --no-install-recommends -y git jq patch && \
     rm -rf /var/lib/apt/lists/* && \
     to_patch=/android-runner && \
     patcher='s/^export LD_PRELOAD=/test "${NO_PRELOAD_CXX:-0}" != 0 || &/' && \