CI: Using more appropriate GitHub Actions syntax to set path (pandas-dev#29983)

Author: datapythonista

.github/workflows/ci.yml

@@ -15,12 +15,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
+    - name: Setting conda path
+      run: echo "::add-path::${HOME}/miniconda3/bin"
+
     - name: Checkout
       uses: actions/checkout@v1
 
-    - name: Setting conda path
-      run: echo "::set-env name=PATH::${HOME}/miniconda3/bin:${PATH}"
-
     - name: Looking for unwanted patterns
       run: ci/code_checks.sh patterns
       if: true