qbs build: Fix spurious re-resolving

The pluginjson module records the VCS state by default, which means qbs
re-resolved the project after every git action. Prevent that.

Change-Id: I24cf1d658ba847b327be018749806856a6e7da1b
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

tests/unit/unittest/unittest.qbs

@@ -27,6 +27,7 @@ CppApplication {
     Depends { name: "gtest"; required: false }
     Depends { name: "gmock"; required: false }
 
+    pluginjson.useVcsData: false
     sqlite_sources.buildSharedLib: false
 
     cpp.defines: {