[bitcoin/bitcoin] appveyor: Run functional test on appveyor (#14007)

MarcoFalke commented on this pull request.

> @@ -5,16 +5,19 @@ configuration: Release
platform: x64
environment:
APPVEYOR_SAVE_CACHE_ON_ERROR: true
-cache: C:\tools\vcpkg\installed\
+ PYTHONIOENCODING: utf-8
+cache:
+- C:\tools\vcpkg\installed
+- build_msvc\cache

I think this caching fix can be submitted in an independent pr