Fix suppressed BouncyCastle known moderate severity vulnerability warning in TlsVariationsExample

[mtmk]

Below is currently suppressed NU1902 https://learn.microsoft.com/en-us/nuget/reference/errors-and-warnings/nu1901-nu1904 because it's an example. We should upgrade the package at some point to avoid any security vulnerability warning for the repo.

src\Samples\TlsVariationsExample\TlsVariationsExample.csproj(0,0): Error NU1902: Warning As Error: Package 'BouncyCastle' 1.8.9 has a known moderate severity vulnerability, https://github.com/advisories/GHSA-8xfc-gm6g-vgpv
src\Samples\TlsVariationsExample\TlsVariationsExample.csproj(0,0): Error NU1902: Warning As Error: Package 'BouncyCastle' 1.8.9 has a known moderate severity vulnerability, https://github.com/advisories/GHSA-m44j-cfrm-g8qc
src\Samples\TlsVariationsExample\TlsVariationsExample.csproj(0,0): Error NU1902: Warning As Error: Package 'BouncyCastle' 1.8.9 has a known moderate severity vulnerability, https://github.com/advisories/GHSA-v435-xc8x-wvr9