Bump XcodeProj version to 7.6.0.

Package.resolved

@@ -87,8 +87,8 @@
         "repositoryURL": "https://github.com/tuist/XcodeProj",
         "state": {
           "branch": null,
-          "revision": "23f7e12a7e0db29b4f16052692d99f9fbe41fa15",
-          "version": "7.5.0"
+          "revision": "02e4ee305baf0ba23af7522210250d8275200122",
+          "version": "7.6.0"
         }
       }
     ]

Package.swift

@@ -27,7 +27,7 @@ let package = Package(
                  targets: ["TuistGenerator"]),
     ],
     dependencies: [
-        .package(url: "https://github.com/tuist/XcodeProj", .upToNextMajor(from: "7.5.0")),
+        .package(url: "https://github.com/tuist/XcodeProj", .upToNextMajor(from: "7.6.0")),
         .package(url: "https://github.com/apple/swift-package-manager", .upToNextMajor(from: "0.5.0")),
         .package(url: "https://github.com/IBM-Swift/BlueSignals", .upToNextMajor(from: "1.0.21")),
         .package(url: "https://github.com/ReactiveX/RxSwift.git", .upToNextMajor(from: "5.0.1")),

Sources/TuistGenerator/Generator/ProjectGenerator.swift

@@ -220,7 +220,7 @@ final class ProjectGenerator: ProjectGenerating {
                 continue
             }
 
-            var attributes = pbxProject.targetAttributes[testTarget] ?? [:]
+            var attributes = pbxProject.targetAttributes?[testTarget] ?? [:]
 
             attributes["TestTargetID"] = target