[skip ci] use symbolic full name for BRANCH in dockerbuild.sh
#!/bin/sh
-docker build --build-arg COMMIT=$(git rev-parse HEAD) --build-arg BRANCH=$(git rev-parse --abbrev-ref HEAD) -t ghcr.io/nh-server/kurisu .
+docker build --build-arg COMMIT=$(git rev-parse HEAD) --build-arg BRANCH=$(git rev-parse --symbolic-full-name HEAD) -t ghcr.io/nh-server/kurisu .
