Update GitHub workflow with deprecated add-path

Author: atoomic

.github/workflows/testsuite.yml

@@ -115,7 +115,7 @@ jobs:
       - name: Set up Perl
         run: |
           choco install strawberryperl
-          echo "##[add-path]C:\strawberry\c\bin;C:\strawberry\perl\site\bin;C:\strawberry\perl\bin"
+          echo "C:\strawberry\c\bin;C:\strawberry\perl\site\bin;C:\strawberry\perl\bin" >> $GITHUB_PATH
       - name: perl -V
         run: perl -V
       - run: perl Makefile.PL