Adding back branch specification just in case.

docker/Dockerfile

@@ -42,6 +42,11 @@ RUN make install
 # Shairport Sync Build System:
 FROM builder-base AS builder-sps
 
+# This will be modified by the Github Action Workflow and is required
+# to ensure the correct branch is being used.
+ARG SHAIRPORT_SYNC_BRANCH
+RUN test -n "$SHAIRPORT_SYNC_BRANCH"
+
 COPY --from=builder-alac /usr/local/lib/libalac.* /usr/local/lib/
 COPY --from=builder-alac /usr/local/lib/pkgconfig/alac.pc /usr/local/lib/pkgconfig/alac.pc
 COPY --from=builder-alac /usr/local/include /usr/local/include
@@ -61,6 +66,7 @@ WORKDIR /
 
 WORKDIR /shairport-sync
 COPY . .
+RUN git checkout $SHAIRPORT_SYNC_BRANCH
 RUN git submodule init
 RUN git submodule update
 RUN autoreconf -fi

docker/README.md

@@ -6,5 +6,7 @@ Available at: https://hub.docker.com/r/mikebrady/shairport-sync
 
 TODO: remove `--ssh` when going public as this is only for private repos.
 ```
-docker buildx build --ssh github=$SSH_AUTH_SOCK --platform linux/arm/v7 -f ./docker/Dockerfile -t registry.nova.do/shairport-sync:unstable-development .
-```
+docker buildx build --ssh github=$SSH_AUTH_SOCK --platform linux/arm/v7 -f ./docker/Dockerfile --build-arg SHAIRPORT_SYNC_BRANCH=charles-dev -t registry.nova.do/shairport-sync:unstable-development .
+```
+
+`SHAIRPORT_SYNC_BRANCH` is required to ensure the image is built using the expected branch.