switch to manual trigger to avoid malicious codes

.github/workflows/pr_test_linux.yaml

 name: pr_test_linux
 
 on:
-  workflow_dispatch: # launch manually for now since there is no sandbox.
+  workflow_dispatch:
+    inputs:
+      test_target:
+        description: 'What to test: "pr" or "branch"'
+        required: true
+        type: choice
+        options:
+          - pr
+          - branch
+
+      pr_number:
+        description: 'Pull Request Number (only if test_target == "pr")'
+        required: false
+
+      branch_name:
+        description: 'Branch name (only if test_target == "branch")'
+        default: 'main'
+        required: false
 #  push:
 #    branches: [ main ]
 #    paths:
@@ -47,10 +64,19 @@ jobs:
     if: ${{ github.event_name != 'issue_comment' || needs.check-comment.outputs.should_run == 'true' }}
 
     steps:
+      - name: Determine ref
+        id: set-ref
+        run: |
+          if [[ "${{ github.event.inputs.test_target }}" == "pr" ]]; then
+            echo "ref=refs/pull/${{ github.event.inputs.pr_number }}/merge" >> $GITHUB_OUTPUT
+          else
+            echo "ref=refs/heads/${{ github.event.inputs.branch_name }}" >> $GITHUB_OUTPUT
+          fi
       - name: Checkout
         uses: actions/checkout@v4
         with:
           #          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ steps.set-ref.outputs.ref }}
           submodules: true
 
       - name: Show current commit
@@ -102,7 +128,7 @@ jobs:
           source $(conda info --base)/etc/profile.d/conda.sh
           conda activate test_env || { echo "Failed to activate conda env"; exit 1; }
           which python
-          NUNCHAKU_TEST_CACHE_ROOT=${{ secrets.NUNCHAKU_TEST_CACHE_ROOT }} HF_TOKEN=${{ secrets.HF_TOKEN }} pytest -v tests/flux/test_flux_memory.py
+          NUNCHAKU_TEST_CACHE_ROOT=${{ secrets.NUNCHAKU_TEST_CACHE_ROOT_LINUX }} HF_TOKEN=${{ secrets.HF_TOKEN }} pytest -v tests/flux/test_flux_memory.py
 
   test-flux-other:
     needs: build
@@ -117,7 +143,7 @@ jobs:
           source $(conda info --base)/etc/profile.d/conda.sh
           conda activate test_env || { echo "Failed to activate conda env"; exit 1; }
           which python
-          NUNCHAKU_TEST_CACHE_ROOT=${{ secrets.NUNCHAKU_TEST_CACHE_ROOT }} HF_TOKEN=${{ secrets.HF_TOKEN }} pytest -v tests/flux --ignore=tests/flux/test_flux_memory.py
+          NUNCHAKU_TEST_CACHE_ROOT=${{ secrets.NUNCHAKU_TEST_CACHE_ROOT_LINUX }} HF_TOKEN=${{ secrets.HF_TOKEN }} pytest -v tests/flux --ignore=tests/flux/test_flux_memory.py
 
   test-sana:
     needs: build
@@ -132,7 +158,7 @@ jobs:
           source $(conda info --base)/etc/profile.d/conda.sh
           conda activate test_env || { echo "Failed to activate conda env"; exit 1; }
           which python
-          NUNCHAKU_TEST_CACHE_ROOT=${{ secrets.NUNCHAKU_TEST_CACHE_ROOT }} HF_TOKEN=${{ secrets.HF_TOKEN }} pytest -v tests/sana
+          NUNCHAKU_TEST_CACHE_ROOT=${{ secrets.NUNCHAKU_TEST_CACHE_ROOT_LINUX }} HF_TOKEN=${{ secrets.HF_TOKEN }} pytest -v tests/sana
 
   clean-up:
     if: always() && (github.event_name != 'issue_comment' || needs.check-comment.outputs.should_run == 'true')