Tests: avoid abnormal exit on failure

Rather than using the forced unwrap, use `XCTUnwrap` to allow the test
suite to continue in the case of a failure.

Author: compnerd

Tests/WorkspaceTests/WorkspaceTests.swift

@@ -5017,7 +5017,7 @@ final class WorkspaceTests: XCTestCase {
         do {
             let ws = try workspace.getOrCreateWorkspace()
             let pinsStore = try ws.pinsStore.load()
-            let fooPin = pinsStore.pins.values.first(where: { $0.packageRef.identity.description == "foo" })!
+            let fooPin = try XCTUnwrap(pinsStore.pins.values.first(where: { $0.packageRef.identity.description == "foo" }))
 
             let fooRepo = workspace.repositoryProvider
                 .specifierMap[RepositorySpecifier(path: try AbsolutePath(