cmd/fix, x/tools/go/analysis: fix can print "applied 8 of 10 fixes; 2 files updated" and fail without actually applying any fixes [1.26 backport]

[gopherbot]

@dmitshur requested issue #77482 to be considered for backport to the next 1.26 minor release.

@gopherbot Please create a backport issue for Go 1.26 (original request was in #77482 (comment)).

[dmitshur]

We reviewed and approved this during a release meeting, moved CherryPickApproved from #77482 (comment) to this issue.