CMake: Fix building samples without webready (backport #2963)

[mergify[bot]]

If EXIV2_ENABLE_WEBREADY is false, the conntest sample can't be built, as its code depends on Exiv2::http which doesn't exist in a non-webready build.

Fixes #2961

---

This is an automatic backport of pull request #2963 done by Mergify.

[mergify[bot]]

Cherry-pick of 79eb7675d8b846c3e89359b92394d6c03a392cba has failed:

On branch mergify/bp/0.28.x/pr-2963
Your branch is up to date with 'origin/0.28.x'.

You are currently cherry-picking commit 79eb7675d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   samples/CMakeLists.txt

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally