add correct base class to OpenSSL::Digest

some method definitions, like OpenSSL::Digest#file, are missing otherwise

Author: HoneyryderChuck

stdlib/openssl/0/manifest.yaml

@@ -1,2 +1,3 @@
 dependencies:
   - name: socket
+  - name: digest

stdlib/openssl/0/openssl.rbs

@@ -3164,7 +3164,8 @@ module OpenSSL
   #     sha256.reset
   #     digest2 = sha256.digest(data2)
   #
-  class Digest
+  class Digest < ::Digest::Class
+
     # <!--
     #   rdoc-file=ext/openssl/lib/openssl/digest.rb
     #   - digest(name, data)