gh-120762: make_ssl_certs: Don't set extensions for the temporary CSR (GH-125045)

gh-120762: make_ssl_certs: Don't set extensions for the CSR

`openssl req` fails with openssl 3.2.2 because the config line

    authorityKeyIdentifier = keyid:always,issuer:always

is not supported for certificate signing requests (since the issuing
certificate authority is not known).

David von Oheimb, the OpenSSL dev that made the change, commented in:
https://github.com/openssl/openssl/issues/22966#issuecomment-1858396738 :

> This problem did not show up in older OpenSSL versions because of a bug:
> the `req` app ignored the `-extensions` option unless `-x505` is given,
> which I fixed in https://github.com/openssl/openssl/pull/16865.

(I assume `-x505` is a typo for `-x509`.)

In our `make_cert_key` function:

If `sign` is true:
- We don't pass `-x509` to `req`, so in this case it should be safe to
  omit the `-extensions` argument. (Old OpenSSL ignores it, new OpenSSL
  fails on it.)
- The extensions are passed to the `ca` call later in the function.
  There they take effect, and `authorityKeyIdentifier` is valid.

If `sign` is false, this commit has no effect except rearranging the
CLI arguments.