appveyor.yml: workaround wrong command line escape

backslash in %APPVEYOR_BUILD_FOLDER% is somehow dropped somewhere
when being passed to test runner via mingw32-make.

Anyway we know the relative path to the project directory, so we can
specify that with slash.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65262 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

appveyor.yml

@@ -137,5 +137,5 @@ for:
     - mingw32-make test
     - mingw32-make test-all TESTOPTS="--retry --job-status=normal --show-skip --subprocess-timeout-scale=1.5 -j %JOBS% --exclude win32ole"
     # separately execute tests that may crash worker without -j.
-    - mingw32-make test-all TESTOPTS="--retry --job-status=normal --show-skip --subprocess-timeout-scale=1.5" TESTS="%APPVEYOR_BUILD_FOLDER%/test/win32ole"
+    - mingw32-make test-all TESTOPTS="--retry --job-status=normal --show-skip --subprocess-timeout-scale=1.5" TESTS="../ruby/test/win32ole"
     - mingw32-make test-spec MSPECOPT=-j