Declare outer trace env vars as final

Author: Luke Daley

Sources/SWBTaskExecution/TaskActions/ClangCompileTaskAction.swift

@@ -460,7 +460,7 @@ public final class ClangNonModularCompileTaskAction: TaskAction {
     private struct ClangAdapter: TaskDependencyVerification.Adapter {
         typealias T = TraceData
 
-        var outerTraceFileEnvVar = "CC_PRINT_HEADERS_FILE"
+        let outerTraceFileEnvVar = "CC_PRINT_HEADERS_FILE"
 
         func exec(ctx: TaskExecutionContext, env: [String : String]) async throws -> CommandResult {
             var env = env

Sources/SWBTaskExecution/TaskActions/LdTaskAction.swift

@@ -41,7 +41,7 @@ public final class LdTaskAction: TaskAction {
     private struct LdAdapter: TaskDependencyVerification.Adapter {
         typealias T = TraceData
 
-        var outerTraceFileEnvVar = "LD_TRACE_FILE"
+        let outerTraceFileEnvVar = "LD_TRACE_FILE"
 
         private static let inherentDependencies = [
             "libSystem.B.tbd",