avoid using set-env in continuous integration workflow

Error: Unable to process command '::set-env name=PROJECT_NAME_LOWER::gzdoom' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

.github/workflows/continuous_integration.yml

@@ -25,17 +25,15 @@ jobs:
     steps:
     - uses: actions/checkout@v1
 
-    - name: Configure
-      run: |
-        echo "::set-env name=PROJECT_NAME_LOWER::$(echo ${{ matrix.config.name }} | tr '[:upper:]' '[:lower:]')"
-
     - name: Build
       run: |
+        PROJECT_NAME_LOWER=$(echo ${{ matrix.config.name }} | tr '[:upper:]' '[:lower:]')
         ./build.py --target ${PROJECT_NAME_LOWER}
 
     - name: Create Package
       shell: bash
       run: |
+        PROJECT_NAME_LOWER=$(echo ${{ matrix.config.name }} | tr '[:upper:]' '[:lower:]')
         if [ -z ${{ matrix.config.bundle }} ]; then
           BUNDLE_FILENAME=${PROJECT_NAME_LOWER}
         else