Mod run tests as embedded package on CI

In Linux editor, there is a problem that assets in local packages cannot be found with `AssetDatabase.FindAssets`.
As a workaround, I have made it into an embedded package.

.github/workflows/test.yml

@@ -42,12 +42,6 @@ jobs:
             octocov: true
 
     steps:
-      - name: Checkout repository
-        uses: actions/checkout@v4
-        with:
-          submodules: false
-          lfs: false
-
       - name: Crete project for tests
         uses: nowsprinting/create-unity-project-action@v3
         with:
@@ -60,17 +54,21 @@ jobs:
           restore-keys: |
             Library-
 
-      - name: Set package name
-        run: |
-          echo "package_name=$(grep -o -E '"name": "(.+)"' ./package.json | cut -d ' ' -f2)" >> "$GITHUB_ENV"
+      - name: Checkout repository as embedded package
+        uses: actions/checkout@v4
+        with:
+          submodules: false
+          lfs: false
+          path: ${{ env.CREATED_PROJECT_PATH }}/Packages/com.nowsprinting.test-helper
+          # In Linux editor, there is a problem that assets in local packages cannot be found with `AssetDatabase.FindAssets`.
+          # As a workaround, I have made it into an embedded package.
 
       - name: Install dependencies
         run: |
           npm install -g openupm-cli
           openupm add -f com.unity.test-framework
           openupm add -f com.unity.testtools.codecoverage
           openupm add -f com.cysharp.unitask
-          openupm add -ft "${{ env.package_name }}"@file:../../
         working-directory: ${{ env.CREATED_PROJECT_PATH }}
 
       - name: Set coverage assembly filters