-warnings-as-errors needs just one dash

Author: fabianfett

.github/workflows/pull_request.yml

@@ -17,10 +17,10 @@ jobs:
         uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
         with:
             linux_5_8_enabled: false
-            linux_5_9_arguments_override: "-Xswiftc --warnings-as-errors --explicit-target-dependency-import-check error"
-            linux_5_10_arguments_override: "-Xswiftc --warnings-as-errors --explicit-target-dependency-import-check error"
-            linux_nightly_6_0_arguments_override: "-Xswiftc --warnings-as-errors --explicit-target-dependency-import-check error"
-            linux_nightly_main_arguments_override: "-Xswiftc --warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_5_9_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_nightly_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_nightly_main_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
 
     swift-6-language-mode:
         name: Swift 6 Language Mode