ci: Enable a subset of the unit tests

The smoke tests need a registry as a test fixture.   We don't yet
have that but until we do we can still run the other tests.

This will ensure that the code builds and some of the functionality
is exercised for each pull request.

Author: euanh

.github/workflows/pull_request.yml

@@ -14,6 +14,16 @@ jobs:
             license_header_check_project_name: "SwiftContainerPlugin"
             shell_check_container_image: "swift:6.0-noble"
 
+    unit-tests:
+        name: Unit tests
+        uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
+        with:
+            linux_5_8_enabled: false
+            linux_5_9_enabled: false
+            linux_5_10_enabled: false
+            linux_nightly_6_0_arguments_override: "--filter 'AuthTests|ReferenceTests'"
+            linux_nightly_main_arguments_override: "--filter 'AuthTests|ReferenceTests'"
+
     swift-6-language-mode:
         name: Swift 6 Language Mode
         uses: apple/swift-nio/.github/workflows/swift_6_language_mode.yml@main

Tests/ContainerRegistryTests/ImageReferenceTests.swift

@@ -27,7 +27,7 @@ struct ReferenceTestCase {
 }
 
 class ReferenceTests: XCTestCase {
-    var tests = [
+    let tests = [
         // A reference which does not contain a '/' is always interpreted as a repository name
         // in the default registry.
         ReferenceTestCase(