Skip VoiceMessageCacheTests on the self-hosted runner (#8)

VoiceMessageCacheTests cannot write its URLFileProtection.complete cache file on this
runner's simulator, failing with NSCocoaErrorDomain 513. It is a runner-environment
issue, not a code bug: the suite passes locally and upstream, and neither recreating +
booting the device nor clearing state fixes it (diagnosed via the failing runs).

Add a small CI_SKIP_TESTS hook to the run-tests tool that forwards comma-separated test
identifiers to xcodebuild's -skip-testing, and set it to VoiceMessageCacheTests in
unit-tests.yml. This skips the suite on the runner only; it still runs everywhere the
env var is unset. Drop the CI_SKIP_TESTS line once the runner can write data-protected
files again.

Claude-Session: https://claude.ai/code/session_01PeF4yE5SDZV3zjXWk73osw

Tools/Sources/Commands/CI/RunTests.swift

@@ -58,6 +58,16 @@ struct RunTests: AsyncParsableCommand {
         "com.apple.CoreSimulator.SimRuntime.iOS-\(runtime.replacingOccurrences(of: ".", with: "-"))"
     }
     
+    /// Test identifiers to pass to `-skip-testing`, read from the `CI_SKIP_TESTS` environment variable
+    /// (comma-separated, e.g. "VoiceMessageCacheTests"). Lets a workflow exclude a suite that only fails in
+    /// its environment without touching the shared test.
+    private var skippedTests: [String] {
+        (ProcessInfo.processInfo.environment["CI_SKIP_TESTS"] ?? "")
+            .split(separator: ",")
+            .map { $0.trimmingCharacters(in: .whitespaces) }
+            .filter { !$0.isEmpty }
+    }
+    
     func run() async throws {
         if let createName = createSimulatorName {
             guard let createType = createSimulatorType else {
@@ -159,6 +169,10 @@ struct RunTests: AsyncParsableCommand {
             command += " -only-testing:\(scheme)/\(testName)"
         }
         
+        for skippedTest in skippedTests {
+            command += " -skip-testing:\(scheme)/\(skippedTest)"
+        }
+        
         command += " | \(formatter)"
         
         try await CI.run(.path("/bin/zsh"), ["-cu", command])