Remove superfluous container authorization from release workflow

The "release" GitHub Actions workflow cross-compiles AVRDUDE in a container.

At the time the workflow was written, the arduino/crossbuild container was configured as private, meaning it was
necessary to configure the workflow to use a personal access token from an account with the necessary permissions in the
`arduino` GitHub organization in order for it to be able to run.

Since that time, the container has been made public. The configuration of the workflow to provide credentials for
container access is now superfluous, making the workflow more difficult for use by contributors and reuse by the
community, and increasing the project's maintenance burden and potential attack surface through the presence of an
unnecessary token.

This unnecessary workflow configuration is hereby removed, taking advantage of the new possibility of pulling the
container anonymously.

Author: per1234

.github/workflows/release.yml

@@ -46,9 +46,6 @@ jobs:
 
     container:
       image: ghcr.io/arduino/crossbuild:0.2.1
-      credentials:
-        username: ${{ github.actor }}
-        password: ${{ secrets.AVRDUDE_CI_PAT }}
 
     steps:
     # the tag must be formatted this way <AVRDUDE_TAG>-arduino.<ARDUINO_VERSION>, e.g tag -> 7.0-arduino.1