mask out tests that are failing on Linux (#996)

Author: QuietMisdreavus

Tests/SwiftDocCTests/LinkTargets/LinkDestinationSummaryTests.swift

@@ -436,7 +436,9 @@ class ExternalLinkableTests: XCTestCase {
             XCTAssertEqual(decoded, summary)
         }
     }
-    
+
+    // TODO: Remove this #if once https://github.com/apple/swift-corelibs-foundation/issues/5028 is resolved
+    #if os(macOS)
     func testVariantSummaries() throws {
         let (bundle, context) = try testBundleAndContext(named: "MixedLanguageFramework")
         let converter = DocumentationNodeConverter(bundle: bundle, context: context)
@@ -591,7 +593,8 @@ class ExternalLinkableTests: XCTestCase {
             XCTAssertEqual(decoded, summary)
         }
     }
-    
+    #endif
+
     func testDecodingLegacyData() throws {
         let legacyData = """
         {

Tests/SwiftDocCUtilitiesTests/ConvertActionTests.swift

@@ -17,7 +17,8 @@ import Markdown
 @testable import SwiftDocCTestUtilities
 
 class ConvertActionTests: XCTestCase {
-    #if !os(iOS)
+    // TODO: Change this back to `#if !os(iOS)` once https://github.com/apple/swift-corelibs-foundation/issues/5028 is resolved
+    #if os(macOS)
     let imageFile = Bundle.module.url(
         forResource: "TestBundle", withExtension: "docc", subdirectory: "Test Bundles")!
         .appendingPathComponent("figure1.png")