build: Fix libssh2 source build (#59164)
Addresses the same CI failure that
https://github.com/JuliaLang/julia/pull/59141 was intended to address.
The issue here is twofold. First, in a source build, we failed to
install openssl header files. Second, even if we had done this, libssh
needs to be explicitly told where to find openssl, otherwise it might
prefer systme files.
(cherry picked from commit 5ddd7215951d096d4bad0f5e153a18930ed39576)