[xdg_directories] Mark as Linux-only (#643)

diff --git a/packages/xdg_directories/CHANGELOG.md b/packages/xdg_directories/CHANGELOG.md
index 1a525f0..53cce62 100644
--- a/packages/xdg_directories/CHANGELOG.md
+++ b/packages/xdg_directories/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.2.0+1
+
+* Marks the package as Linux-only using the new Dart `platforms` key.
+
 ## 0.2.0
 
 * Migrated to null safety.
diff --git a/packages/xdg_directories/pubspec.yaml b/packages/xdg_directories/pubspec.yaml
index 12eed83..11b01bd 100644
--- a/packages/xdg_directories/pubspec.yaml
+++ b/packages/xdg_directories/pubspec.yaml
@@ -2,11 +2,14 @@
 description: A Dart package for reading XDG directory configuration information on Linux.
 repository: https://github.com/flutter/packages/tree/main/packages/xdg_directories
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+xdg_directories%22
-version: 0.2.0
+version: 0.2.0+1
 
 environment:
   sdk: ">=2.12.0 <3.0.0"
 
+platforms:
+  linux:
+
 dependencies:
   meta: ^1.3.0
   path: ^1.8.0