Default to TS's polling watcher for our tests

The filesystem watcher (which they changed to by default in TS 4.9) is
just too unstable in the GH Actions runner for us to count on.

test-packages/test-utils/src/project.ts

@@ -17,6 +17,7 @@ const ROOT = pathUtils.normalizeFilePath(path.resolve(dirname, '../../ephemeral'
 interface TsconfigWithGlint {
   extends?: string;
   compilerOptions?: Record<string, unknown>; // no appropriate types exist :sigh:
+  watchOptions?: Record<string, unknown>; // https://www.typescriptlang.org/tsconfig#watchOptions
   references?: Array<{ path: string }>;
   files?: Array<string>;
   include?: Array<string>;
@@ -69,7 +70,7 @@ export class Project {
     }
 
     let project = new Project(rootDir);
-    let tsconfig = {
+    let tsconfig: TsconfigWithGlint = {
       compilerOptions: {
         strict: true,
         target: 'es2019',
@@ -80,6 +81,11 @@ export class Project {
         checkJs: false,
         ...config.compilerOptions,
       },
+      watchOptions: {
+        watchFile: 'fixedPollingInterval',
+        watchDirectory: 'fixedPollingInterval',
+        synchronousWatchDirectory: true,
+      },
       glint: config.glint ?? {
         environment: 'glimmerx',
       },