Dockerfile: Rebase on Flathub actions image (#234)

Author: ryonakano

Dockerfile

@@ -1,27 +1,6 @@
-FROM ubuntu:latest
-
-ARG TARGETARCH
-
-ENV DEBIAN_FRONTEND=noninteractive
-
-RUN apt-get update && \
-    apt-get -y install curl flatpak flatpak-builder python3-aiohttp python3-tenacity python3-gi libostree-dev xvfb ccache zstd docker.io && \
-    apt-get -y autoremove && \
-    apt-get autoclean && \
-    rm -rf /var/lib/apt/lists/*
+# Base on the official Docker image for CI by Flathub to use patched version of AppStream
+# that propagates all custom tags in .metainfo files.
+# See https://github.com/flatpak/flatpak-builder/pull/735
+FROM ghcr.io/flathub-infra/flatpak-github-actions:gnome-50
 
 RUN flatpak remote-add --if-not-exists appcenter https://flatpak.elementary.io/repo.flatpakrepo
-
-RUN curl -L https://github.com/flatpak/flat-manager/releases/download/0.5.0/flat-manager-client.$TARGETARCH -o ./flat-manager-client
-
-RUN SHA256_EXPECTED=$( \
-        case $TARGETARCH in \
-            amd64) echo "9733a148ac185bc8d7fb0429a43f9ad7d934635760bb71933658642c697f87c9";; \
-            arm64) echo "fa9a916badc539ff7319895789f004dc99b81eb8e90a75857232121650335956";; \
-        esac \
-    ) && \
-    SHA256_CALC=$(sha256sum ./flat-manager-client | awk '{ print $1 }') && \
-    [ "$SHA256_CALC" = "$SHA256_EXPECTED" ]
-
-RUN mv ./flat-manager-client /usr/bin/flat-manager-client
-RUN chmod +x /usr/bin/flat-manager-client