Add testdata cache folder to .gitignore

Author: nyalldawson

.gitignore

@@ -51,6 +51,7 @@ scripts/astyle.exe
 scripts/Debug
 scripts/qgisstyle*
 scripts/RelWithDebInfo
+tests/testdata/cache/
 tests/testdata/checker360by180.asc.aux.xml
 tests/testdata/grass/wgs84/test/.gislock
 tests/testdata/grass/wgs84/test6/.gislock