CI Fix: Pass --user-data-dir to keep mac CI IPC socket path under 103 chars (#5514)

The default --user-data-dir lives under .vscode-test/, which combined
with the nested checkout paths CI uses pushes the main IPC socket
(<user-data-dir>/<version>-main.sock) over the macOS 103-char AF_UNIX
limit. VS Code prints the warning, Server.listen() fails with EINVAL,
tests never start. Pointing the option at os.tmpdir() shortens the path
under the limit. Windows uses named pipes so it's unaffected; Linux's
limit is roomier but the shorter path doesn't hurt.

See microsoft/vscode#196543 for the same bug from 2023.

Co-authored-by: Jakub Jares <jajares@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

.vscode-test.mjs

@@ -1,5 +1,7 @@
 import { defineConfig } from "@vscode/test-cli";
 import { existsSync } from "fs";
+import { tmpdir } from "os";
+import { join } from "path";
 
 export default defineConfig({
     files: "test/**/*.test.ts",
@@ -10,6 +12,11 @@ export default defineConfig({
         "--disable-extensions",
         // Undocumented but valid option to use a temporary profile for testing
         "--profile-temp",
+        // Keep the user-data-dir short. The default lives under .vscode-test/
+        // which, combined with the nested checkout paths CI uses, can push the
+        // main IPC socket path over the macOS 103-char AF_UNIX limit and fail
+        // with EINVAL. See microsoft/vscode#196543.
+        `--user-data-dir=${join(tmpdir(), "vscp")}`,
     ],
     workspaceFolder: `test/${existsSync("C:\\powershell-7\\pwsh.exe") ? "OneBranch" : "TestEnvironment"}.code-workspace`,
     mocha: {