ptest-packagelists.inc: Add python3-license-expression

 # ./run-ptest
     [snip]
     PASS: tests/test_license_expression.py::LicensingValidateTest::test_validation_bad_syntax
     PASS: tests/test_license_expression.py::LicensingValidateTest::test_validation_exception_as_regular_key
     PASS: tests/test_license_expression.py::LicensingValidateTest::test_validation_exception_with_choice
     PASS: tests/test_license_expression.py::LicensingValidateTest::test_validation_invalid_license_exception
     PASS: tests/test_license_expression.py::LicensingValidateTest::test_validation_invalid_license_exception_strict_false
     PASS: tests/test_license_expression.py::LicensingValidateTest::test_validation_invalid_license_key
     PASS: tests/test_license_expression.py::UtilTest::test_build_licensing
     PASS: tests/test_license_expression.py::UtilTest::test_build_spdx_licensing
     PASS: tests/test_license_expression.py::UtilTest::test_get_license_key_info
     PASS: tests/test_license_expression.py::UtilTest::test_get_license_key_info_vendored
     PASS: tests/test_license_expression.py::CombineExpressionTest::test_combine_expressions_with_duplicated_elements
     PASS: tests/test_license_expression.py::CombineExpressionTest::test_combine_expressions_with_empty_input
     PASS: tests/test_license_expression.py::CombineExpressionTest::test_combine_expressions_with_or_relationship
     PASS: tests/test_license_expression.py::CombineExpressionTest::test_combine_expressions_with_regular
     PASS: tests/test_skeleton_codestyle.py::BaseTests::test_skeleton_codestyle
    ============================================================================
    Testsuite summary
     # TOTAL: 175
     # PASS: 175
     # SKIP: 0
     # XFAIL: 0
     # FAIL: 0
     # XPASS: 0

Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>