fix: use JAVA_TOOL_OPTIONS to set user.home for sandbox JVM

tools.deps uses System.getProperty("user.home") to find the Maven
local repo, not maven.repo.local. CLJ_JVM_OPTS may not reach the
tools JVM either. JAVA_TOOL_OPTIONS is universally applied to all
JVM processes, so -Duser.home=/home/runner ensures the tools JVM
finds the mounted .m2/repository at the correct absolute path.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: krukow

.github/workflows/copilot-setup-steps.yml

@@ -73,7 +73,7 @@ jobs:
           # at those same absolute paths. Set env vars so bb's deps.clj
           # and the tools JVM use the absolute host paths instead of $HOME.
           echo "DEPS_CLJ_TOOLS_DIR=$HOME/.deps.clj" >> "$GITHUB_ENV"
-          echo "CLJ_JVM_OPTS=-Dmaven.repo.local=$HOME/.m2/repository" >> "$GITHUB_ENV"
+          echo "JAVA_TOOL_OPTIONS=-Duser.home=$HOME" >> "$GITHUB_ENV"
           # Ensure deps directories are readable by any user
           chmod -R a+rX ~/.m2/repository ~/.deps.clj 2>/dev/null || true
       - name: Install gh-aw extension