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

[mergify]

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

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This is an automatic backport of pull request #2963 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 79eb767 has failed:

On branch mergify/bp/0.28.x/pr-2963
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You are currently cherry-picking commit 79eb7675d.
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Unmerged paths:
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	both modified:   samples/CMakeLists.txt

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