[llvm] [Github][Docker] Remove 'docker.io/library' from image name (PR #162007)

[Tom Stellard via llvm-commits]

tstellar wrote:

@boomanaiden154 The short names make it easier for an attacker to spoof an image.  Here is an article about it: https://www.redhat.com/en/blog/be-careful-when-pulling-images-short-name


https://github.com/llvm/llvm-project/pull/162007