Basically revert changes to test framework build script + Dockerfile

test/Dockerfile

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

test/build.sh

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