Fix nightly smoke test failure (#468)

Author: cmcgee1024

Tests/SwiftlyTests/CommandLineTests.swift

@@ -270,8 +270,9 @@ public struct CommandLineTests {
     func testSwift() async throws {
         let tmp = fs.mktemp()
         try await fs.mkdir(atPath: tmp)
-        try await sys.swift().package()._init(.package_path(tmp), .type("executable")).run()
-        try await sys.swift().build(.package_path(tmp), .configuration("release")).run()
+        let swiftExec: Executable = .path(try Executable.name("swift").resolveExecutablePath(in: .inherit))
+        try await sys.swift(executable: swiftExec).package()._init(.package_path(tmp), .type("executable")).run()
+        try await sys.swift(executable: swiftExec).build(.package_path(tmp), .configuration("release")).run()
     }
 
     @Test func testMake() async throws {