Fix python tests (#7960)

* Don't generate types unless --python-typing specified

Fixes https://github.com/google/flatbuffers/issues/7944

* Fix incorrect import statements

Fixes https://github.com/google/flatbuffers/issues/7951

* Fix $PYTHONPATH in PythonTest.sh

Regressed from https://github.com/google/flatbuffers/pull/7529

* PythonTest: fail if something goes wrong

GitHub Actions runs `bash PythonTest.sh`, and thus failures were not
visible.

* Build flatc for Python tests

* Regenerate codes

---------

Co-authored-by: Derek Bailey <derekbailey@google.com>

tests/PythonTest.sh

@@ -1,4 +1,4 @@
-#!/bin/bash -eu
+#!/bin/bash
 #
 # Copyright 2014 Google Inc. All rights reserved.
 #
@@ -14,10 +14,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+set -eu
+
 pushd "$(dirname $0)" >/dev/null
 test_dir="$(pwd)"
 gen_code_path=${test_dir}
-runtime_library_dir=${test_dir}/../../python
+runtime_library_dir=${test_dir}/../python
 
 # Emit Python code for the example schema in the test dir:
 ${test_dir}/../flatc -p -o ${gen_code_path} -I include_test monster_test.fbs --gen-object-api