Fix extension install test

This is not a valid ID (to install a specific version you use @) and,
quite strangely, Code is now returning an "extension not found" error if
the ID is invalid, breaking the test since we expect it to error about
the marketplace not existing.

test/integration/installExtension.test.ts

@@ -12,7 +12,7 @@ describe("--install-extension", () => {
     setupFlags = ["--extensions-dir", tempDir]
   })
   it("should use EXTENSIONS_GALLERY when set", async () => {
-    const extName = `author.extension-1.0.0`
+    const extName = "author.extension"
     const { stderr } = await runCodeServerCommand([...setupFlags, "--install-extension", extName], {
       EXTENSIONS_GALLERY: "{}",
     })