Use app build container for building test runner

test/Dockerfile

@@ -1,6 +1,2 @@
-FROM debian:stable
-
-RUN apt-get update && apt-get install -y \
-    gcc curl libdbus-1-dev protobuf-compiler
-RUN curl https://sh.rustup.rs -sSf | sh -s -- -y
-ENV PATH="/root/.cargo/bin:${PATH}"
+ARG IMAGE=ghcr.io/mullvad/mullvadvpn-app-build:latest
+FROM $IMAGE

test/build.sh

@@ -3,15 +3,17 @@
 set -eu
 
 SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+APP_DIR="$SCRIPT_DIR/.."
 cd "$SCRIPT_DIR"
 
 if [[ $TARGET == x86_64-unknown-linux-gnu ]]; then
     mkdir -p .container/cargo-registry
-    podman build -t mullvadvpn-app-tests .
+    container_image=$(cat "$APP_DIR/building/linux-container-image.txt")
+    podman build -t mullvadvpn-app-tests --build-arg IMAGE="${container_image}" .
 
     podman run --rm -it \
         -v "${SCRIPT_DIR}/.container/cargo-registry":/root/.cargo/registry \
-        -v "${SCRIPT_DIR}/..":/src:Z \
+        -v "${APP_DIR}":/src:Z \
         -e CARGO_HOME=/root/.cargo/registry \
         mullvadvpn-app-tests \
         /bin/bash -c "cd /src/test/; cargo build --bin test-runner --release --target ${TARGET}"