Upload test results to AppVeyor (#1918)

So that it shows up in `Tests` tab, not only `Console`

.appveyor.yml

@@ -66,5 +66,9 @@ install:
 ## Run the actual test
 test_script:
     - cd c:\projects\php-project-workspace
-    - vendor/bin/phpunit
+    - vendor/bin/phpunit --log-junit build/phpunit/phpunit.xml
     - php ./psalm --shepherd
+
+on_finish:
+    - ps: $wc = New-Object 'System.Net.WebClient'
+    - ps: $wc.UploadFile("https://ci.appveyor.com/api/testresults/junit/$($env:APPVEYOR_JOB_ID)", (Resolve-Path .\build\phpunit\phpunit.xml))