chore: fix example test code for appstarter and module

[kenjis]

Description

• fix example test code for starter and module

Right after installing CI4, tests fail:

$ composer create-project codeigniter4/appstarter ci4
$ cd ci4
$ composer test
> phpunit
PHPUnit 9.5.10 by Sebastian Bergmann and contributors.

FEE..                                                               5 / 5 (100%)

Time: 00:00.584, Memory: 26.00 MB

There were 2 errors:

1) ExampleDatabaseTest::testSoftDeleteLeavesRow
ErrorException: Attempt to read property "id" on null

/Users/kenji/tmp/ci4/tests/database/ExampleDatabaseTest.php:32

2) ExampleSessionTest::testSessionSimple
Error: Call to a member function set() on array

/Users/kenji/tmp/ci4/tests/session/ExampleSessionTest.php:12

--

There was 1 failure:

1) ExampleDatabaseTest::testModelFindAll
Failed asserting that actual size 0 matches expected size 3.

/Users/kenji/tmp/ci4/tests/database/ExampleDatabaseTest.php:22

ERRORS!
Tests: 5, Assertions: 3, Errors: 2, Failures: 1.

Generating code coverage report in Clover XML format ... done [00:00.180]

Generating code coverage report in HTML format ... done [00:00.184]

Generating code coverage report in PHP format ... done [00:00.001]


Code Coverage Report:   
  2021-12-01 05:37:22   
                        
 Summary:               
  Classes: 20.00% (1/5) 
  Methods: 16.67% (1/6) 
  Lines:   20.93% (9/43)

Config\Database
  Methods: 100.00% ( 1/ 1)   Lines: 100.00% (  4/  4)
Script phpunit handling the test event returned with error code 2

Checklist:

• Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• [] User guide updated
• Conforms to style guide