libgit2/test: Handle a partially broken openssl install (#60035)
The path to the openssl config file gets baked in at build time and is
wrong for the openssl we ship in JLLs causing trouble here if there is
no systemwide openssl. However, for our purposes an empty openssl cnf is
fine and probably better for reproducability anyway, so just set that.
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Co-authored-by: Keno Fischer <Keno@users.noreply.github.com>
