CI: Ruby version to 3.4 and PGVER to 17

Author: larskanis

appveyor.yml

@@ -21,8 +21,5 @@ test_script:
 
 environment:
   matrix:
-    # ruby-3.3.6 currently fails installing stringio-3.1.5.gem
-    # - ruby_version: "33-x64"
-      # PGVER: 16
-    - ruby_version: "27-x64"
-      PGVER: 11
+    - ruby_version: "34-x64"
+      PGVER: 17