ci: pass CLI branch via env, not inline (fixes semgrep run-shell-injection)

git clone interpolated github.event.inputs.branch directly into the shell.
Pass it via env ($BRANCH); it is regex-validated upstream. Part of PER-9772.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: pranavz28

.github/workflows/test.yml

@@ -48,9 +48,11 @@ jobs:
           restore-keys: v1/${{ runner.os }}/node-${{ matrix.node }}/
       - name: Set up @percy/cli from git
         if: ${{ github.event_name == 'workflow_dispatch' }}
+        env:
+          BRANCH: ${{ github.event.inputs.branch }}
         run: |
           cd /tmp
-          git clone --branch ${{ github.event.inputs.branch }} --depth 1 https://github.com/percy/cli
+          git clone --branch "$BRANCH" --depth 1 https://github.com/percy/cli
           cd cli
           PERCY_PACKAGES=`find packages -mindepth 1 -maxdepth 1 -type d | sed -e 's/packages/@percy/g' | tr '\n' ' '`
           git log -1