Adds Alpine build CI job to the GitHub actions submit.yml. I can add tests too if people think that would be useful but for now I've left it as just build.
------------- Commit messages: - fix sha256 command - add alpine github action Changes: https://git.openjdk.java.net/jdk/pull/7771/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7771&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8282944 Stats: 107 lines in 2 files changed: 106 ins; 0 del; 1 mod Patch: https://git.openjdk.java.net/jdk/pull/7771.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/7771/head:pull/7771 PR: https://git.openjdk.java.net/jdk/pull/7771