ci(windows): drop Python 3.8 packages

The runner image to build 3.8 package doesn't seem to have a currently
supported database, and the previously used 9.6 is no more supported on
current runners.

Author: dvarrazzo

.appveyor/packages.yml

@@ -19,8 +19,6 @@ environment:
     - {PY_VER: "310", PY_ARCH: "64", APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019}
     - {PY_VER: "39", PY_ARCH: "32", APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019}
     - {PY_VER: "39", PY_ARCH: "64", APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019}
-    - {PY_VER: "38", PY_ARCH: "32", APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015}
-    - {PY_VER: "38", PY_ARCH: "64", APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015}
 
   WORKFLOW: packages
 
@@ -39,14 +37,14 @@ environment:
   PERL5LIB: .
 
   # Select according to the service enabled
-  POSTGRES_DIR: C:\Program Files\PostgreSQL\9.6\
+  POSTGRES_DIR: C:\Program Files\PostgreSQL\13\
 
 matrix:
   fast_finish: false
 
 services:
   # Note: if you change this service also change POSTGRES_DIR
-  - postgresql96
+  - postgresql13
 
 cache:
   # Rebuild cache if following file changes