bpo-33764: Appveyor fixes (GH-7364) (GH-7380)

* Prevent spurious message if taking a shortcut
* Fix YAML style
* Disable largefile tests

.github/appveyor.yml

@@ -20,16 +20,17 @@ before_build:
         If (!$changes) {
           echo 'Only docs were updated, stopping build process.'
           Exit-AppveyorBuild
-        }
+        } else {
           echo 'Doing full build due to non-doc changes in these files:'
           echo $changes
         }
+      }
 
 
 build_script:
   - cmd: PCbuild\build.bat -e
   - cmd: PCbuild\python.exe -m test.pythoninfo
 test_script:
-  - cmd: PCbuild\rt.bat -q -uall -u-cpu -rwW --slowest -j2
+  - cmd: PCbuild\rt.bat -q -uall -u-cpu -u-largefile -rwW --slowest -j2
 environment:
   HOST_PYTHON: C:\Python36\python.exe