Refinements to swift argument selection

Author: AlexNachbaur

.github/actions/setup-swift/action.yaml

@@ -31,6 +31,9 @@ runs:
               echo "Requires the use of \"${swift_arguments}\" Swift arguments"
               echo "SWIFT_ARGUMENTS=${swift_arguments}" >> $GITHUB_ENV
               echo "swift_arguments=${swift_arguments}" >> $GITHUB_OUTPUT
+            else
+              echo "SWIFT_ARGUMENTS=" >> $GITHUB_ENV
+              echo "swift_arguments=" >> $GITHUB_OUTPUT
             fi
 
             exit 0

.github/workflows/tests.yaml

@@ -180,7 +180,7 @@ jobs:
       matrix:
         include:
         - swift_version: "5.10"
-          os: macos-14
+          os: macos-15
         - swift_version: "6.0"
           os: macos-15
         - swift_version: "6.1"