Add /.index-data to .gitignore in InitPackage.swift (#7843)

Resolves #7772

Author: MaxDesiatov

Sources/Workspace/InitPackage.swift

@@ -446,6 +446,7 @@ public final class InitPackage {
                 """
                 .DS_Store
                 /.build
+                /.index-build
                 /Packages
                 xcuserdata/
                 DerivedData/