Integration: Lower default concurrency (#331)

I only see a very small delta halving this (.6 seconds), and the default
will likely stress the CI machines a lot more. This change also swaps
the atomic increments to .relaxed, as there's no ordering required, just
need no torn writes.

Sources/Integration/Suite.swift

@@ -151,7 +151,7 @@ struct IntegrationSuite: AsyncParsableCommand {
     var kernel: String = "./bin/vmlinux"
 
     @Option(name: .shortAndLong, help: "Maximum number of concurrent tests")
-    var maxConcurrency: Int = 8
+    var maxConcurrency: Int = 4
 
     static func binPath(name: String) -> URL {
         URL(fileURLWithPath: FileManager.default.currentDirectoryPath)
@@ -302,10 +302,10 @@ struct IntegrationSuite: AsyncParsableCommand {
                             let lasted = CFAbsoluteTimeGetCurrent() - started
 
                             log.info("✅ test \(job.name) complete in \(lasted)s.")
-                            passed.add(1, ordering: .acquiring)
+                            passed.add(1, ordering: .relaxed)
                         } catch let err as SkipTest {
                             log.info("⏭️ skipped test: \(err)")
-                            skipped.add(1, ordering: .acquiringAndReleasing)
+                            skipped.add(1, ordering: .relaxed)
                         } catch {
                             log.error("❌ test \(job.name) failed: \(error)")
                         }