fix: streamline GIT_SHA and GIT_BRANCH retrieval in docker/common

docker/common

@@ -6,19 +6,11 @@ PACKAGE_NAME=beebop-py
 PACKAGE_ORG=mrcide
 PACKAGE_DEV=dev
 
-# Buildkite doesn't check out a full history from the remote (just the
-# single commit) so you end up with a detached head and git rev-parse
-# doesn't work
-if [ "$BUILDKITE" = "true" ]; then
-    GIT_SHA=${BUILDKITE_COMMIT:0:7}
+GIT_SHA=$(git -C "$PACKAGE_ROOT" rev-parse --short=7 HEAD)
+if [[ -v "BRANCH_NAME" ]]; then
+    GIT_BRANCH=${BRANCH_NAME}
 else
-    GIT_SHA=$(git -C "$PACKAGE_ROOT" rev-parse --short=7 HEAD)
-fi
-
-if [ "$BUILDKITE" = "true" ]; then
-    GIT_BRANCH=$BUILDKITE_BRANCH
-else
-    GIT_BRANCH=$(git -C "$PACKAGE_ROOT" symbolic-ref --short HEAD)
+    GIT_BRANCH=$(git symbolic-ref --short HEAD)
 fi
 
 # production image