ci: Use printf(1) to avoid echo(1) problems

Use printf(1) to avoid possible echo(1) incompatibilities like
special escape sequences and the like.

.github/workflows/build.yml

@@ -114,7 +114,7 @@ jobs:
       - name: Install
         run: sudo cmake --build build --target install
       - name: Dryrun_test
-        run: echo -e \\n | ./tools/test-avrdude -d0 -p"-cdryrun -pm2560" -p"-cdryrun -pavr64du28"        
+        run: printf "\n\n" | ./tools/test-avrdude -d0 -p"-cdryrun -pm2560" -p"-cdryrun -pavr64du28"
       - name: Archive build artifacts
         if: always()
         uses: actions/upload-artifact@v3