Add some comments to explain test case

src/trap-caching.test.ts

@@ -197,47 +197,56 @@ test("download cache looks for the right key and creates dir", async (t) => {
 
 test("cleanup removes only old CodeQL TRAP caches", async (t) => {
   await util.withTmpDir(async (tmpDir) => {
+    // This config specifies that we are analyzing JavaScript and Ruby, but not Swift.
     const config = getTestConfigWithTempDir(tmpDir);
 
     sinon.stub(actionsUtil, "getRef").resolves("refs/heads/main");
     sinon.stub(actionsUtil, "isAnalyzingDefaultBranch").resolves(true);
     const listStub = sinon.stub(apiClient, "listActionsCaches").resolves([
+      // Should be kept, since it's not relevant to CodeQL. In reality, the API shouldn't return
+      // this in the first place, but this is a defensive check.
       {
         id: 1,
         key: "some-other-key",
         created_at: "2024-05-23T14:25:00Z",
         size_in_bytes: 100 * 1024 * 1024,
       },
+      // Should be kept, since it's the newest TRAP cache for JavaScript
       {
         id: 2,
         key: "codeql-trap-1-2.0.0-javascript-newest",
         created_at: "2024-04-23T14:25:00Z",
         size_in_bytes: 50 * 1024 * 1024,
       },
+      // Should be cleaned up
       {
         id: 3,
         key: "codeql-trap-1-2.0.0-javascript-older",
         created_at: "2024-03-22T14:25:00Z",
         size_in_bytes: 200 * 1024 * 1024,
       },
+      // Should be cleaned up
       {
         id: 4,
         key: "codeql-trap-1-2.0.0-javascript-oldest",
         created_at: "2024-02-21T14:25:00Z",
         size_in_bytes: 300 * 1024 * 1024,
       },
+      // Should be kept, since it's the newest TRAP cache for Ruby
       {
         id: 5,
         key: "codeql-trap-1-2.0.0-ruby-newest",
         created_at: "2024-02-20T14:25:00Z",
         size_in_bytes: 300 * 1024 * 1024,
       },
+      // Should be kept, since we aren't analyzing Swift
       {
         id: 6,
         key: "codeql-trap-1-2.0.0-swift-newest",
         created_at: "2024-02-22T14:25:00Z",
         size_in_bytes: 300 * 1024 * 1024,
       },
+      // Should be kept, since we aren't analyzing Swift
       {
         id: 7,
         key: "codeql-trap-1-2.0.0-swift-older",