exclude rustls-cert-gen from semver check

`semver-checks` fail in CI because there is no published version of
`rustls-cert-gen`. excluding it seems like the simplest fix for the
moment. other workarounds can be found here: https://github.com/obi1kenobi/cargo-semver-checks#does-the-crate-im-checking-have-to-be-published-on-cratesio

Author: tbro

.github/workflows/ci.yml

@@ -90,6 +90,8 @@ jobs:
 
       - name: Check semver
         uses: obi1kenobi/cargo-semver-checks-action@v2
+        with:
+          exclude: rustls-cert-gen
 
   build-windows:
     runs-on: windows-latest