Fix build script

.ci/image/Dockerfile.linux

@@ -5,6 +5,7 @@ RUN set -eux; \
     apt-get install --no-install-recommends -y \
         build-essential \
         curl \
+        git \
         gpg \
         jq \
      	libatk1.0-dev \

.ci/tasks/build.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 set -eu
 
@@ -16,7 +16,7 @@ cd "repo"
 
 if [ -n "${PR:-}" ]; then
     title "PR: $(echo "$PR" | jq '.number') - $(echo "$PR" | jq '.title')"
-    ref="pr-$(echo "$PR" | jq '.number')-$(git rev-parse --short $(cat .git/ref || echo "HEAD")) 2>/dev/null || echo 'manual')"
+    ref="pr-$(echo "$PR" | jq '.number')-$(git rev-parse --short "$(cat .git/ref || echo "HEAD")" 2>/dev/null || echo 'manual')"
 else
     ref=$(git describe --tags)
 fi