fix: Use cosmiconfigSync to work around segfault in tests

Consistently running into a segfault coming from Node as a result of
cosmiconfig attempting to run a dynamic import on the listed .js config
file caused by:

nodejs/node#35889
jestjs/jest#11438

Using cosmiconfigSync to workaround this which will fall back to using a
synchronous require() call.

src/config.ts

@@ -1,4 +1,4 @@
-import { cosmiconfig } from 'cosmiconfig';
+import { cosmiconfigSync } from 'cosmiconfig';
 import { ProcessedResult } from './process';
 import { readJson, writeJson } from './fs';
 import { CliArguments, Context, PackageJson } from './index';
@@ -136,8 +136,8 @@ export async function getConfig(args?: CliArguments): Promise<Config> {
     return cachedConfig;
   }
 
-  const cosmiconfigResult = await cosmiconfig('unimported').search();
-  const configFile = (cosmiconfigResult?.config ?? {}) as Partial<UnimportedConfig>;
+  const cosmiconfigResult = cosmiconfigSync('unimported').search();
+  const configFile = cosmiconfigResult?.config as Partial<UnimportedConfig>;
 
   const unimportedPkg = await readPkgUp({ cwd: __dirname });