add global git config entry for GITHUB_WORKSPACE as a safe.directory

Approach suggested by actions/checkout#766 and imitated from @JavidPack's comment in #11

entrypoint.sh

@@ -38,6 +38,7 @@ if [[ "$INPUT_ALLOW_FF" == "true" ]]; then
   fi
 fi
 
+git config --global --add safe.directory "$GITHUB_WORKSPACE"
 git remote set-url origin https://x-access-token:${!INPUT_PUSH_TOKEN}@github.com/$GITHUB_REPOSITORY.git
 git config --global user.name "$INPUT_USER_NAME"
 git config --global user.email "$INPUT_USER_EMAIL"