test: fik flaky fs test (#4764)

Our mkdir() spy was sometimes catching an unexpected mkdir()
call and causing the test to fail.

So instead we are just checking that the first mkdir() call
has the expected args

Signed-off-by: Nikolas Komonen <nkomonen@amazon.com>

packages/core/src/test/srcShared/fs.test.ts

@@ -170,13 +170,13 @@ describe('FileSystem', function () {
         paths.forEach(async function (p) {
             it(`creates folder but uses the "fs" module if in C9: '${p}'`, async function () {
                 sandbox.stub(extensionUtilities, 'isCloud9').returns(true)
-                const mkdirSpy = sandbox.spy(fsPromises, 'mkdir')
                 const dirPath = createTestPath(p)
+                const mkdirSpy = sandbox.spy(fsPromises, 'mkdir')
 
                 await fsCommon.mkdir(dirPath)
 
                 assert(existsSync(dirPath))
-                assert.deepStrictEqual(mkdirSpy.args, [[dirPath, { recursive: true }]])
+                assert.deepStrictEqual(mkdirSpy.args[0], [dirPath, { recursive: true }])
             })
         })
     })