Fix REPO_ROOT computation in run-test.sh

Use `git rev-parse --show-toplevel` instead of fragile relative path.

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

Author: redsun82

rust/ql/lib/upgrades/66a489863649185f4a9770f894505803059a1312/test/run-test.sh

@@ -5,7 +5,7 @@
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-REPO_ROOT="$(cd "$SCRIPT_DIR/../../../../.." && pwd)"
+REPO_ROOT="$(git rev-parse --show-toplevel)"
 OLD_COMMIT="${OLD_COMMIT:-491c373e076}"  # origin/main at time of this upgrade
 
 cd "$REPO_ROOT"