Pin to SwiftSyntax 509.0.0 release (pointfreeco#774)

Author: stephencelis

Package.resolved

@@ -1,16 +1,14 @@
 {
-  "object": {
-    "pins": [
-      {
-        "package": "swift-syntax",
-        "repositoryURL": "https://github.com/apple/swift-syntax.git",
-        "state": {
-          "branch": null,
-          "revision": "7bb5231dad28c6dceabf7a439867f39d2c105e4f",
-          "version": "509.0.0-swift-DEVELOPMENT-SNAPSHOT-2023-09-05-a"
-        }
+  "pins" : [
+    {
+      "identity" : "swift-syntax",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-syntax.git",
+      "state" : {
+        "revision" : "74203046135342e4a4a627476dd6caf8b28fe11b",
+        "version" : "509.0.0"
       }
-    ]
-  },
-  "version": 1
+    }
+  ],
+  "version" : 2
 }

Package.swift

@@ -21,10 +21,7 @@ let package = Package(
     ),
   ],
   dependencies: [
-    .package(
-      url: "https://github.com/apple/swift-syntax.git",
-      from: "509.0.0-swift-DEVELOPMENT-SNAPSHOT-2023-09-05-a"
-    )
+    .package(url: "https://github.com/apple/swift-syntax.git", from: "509.0.0")
   ],
   targets: [
     .target(