Print a message when fetching is skipped for an immutable ref
Print a message when fetching is skipped for an immutable ref

The output indicates that fetching happens even when it is skipped.

To avoid confusion, print a message when fetching is skipped for
an immutable ref so that the user knows when and why a fetch is skipped.

Change-Id: Id6e4812cebc5e57d379feb76a9d034af0b93043b

GerritCodeReview/git-repo,GerritCodeReview/git-repo,TheQtCompany/git-repo,lewixliu/git-repo,codetutil/git-repo,lipro-yocto/git-repo,nuclearmistake/repo,gabbayo/git-repo,wavecomp/git-repo,nuclearmistake/repo,mer-tools/git-repo,lewixliu/git-repo,lipro-yocto/git-repo,mer-tools/git-repo,chenzilin/git-repo,codetutil/git-repo,wavecomp/git-repo,gabbayo/git-repo,couchbasedeps/git-repo,couchbasedeps/git-repo,aosp-mirror/tools_repo,TheQtCompany/git-repo,chenzilin/git-repo,aosp-mirror/tools_repo