add constraint on WTForms (GoogleCloudPlatform#7057)

## Description

Fixes GoogleCloudPlatform#7045
Fixes GoogleCloudPlatform#7046
Fixes GoogleCloudPlatform#7047
Fixes GoogleCloudPlatform#7048
Fixes GoogleCloudPlatform#7049
Fixes GoogleCloudPlatform#7050
Fixes GoogleCloudPlatform#7051
Fixes GoogleCloudPlatform#7052 
Fixes GoogleCloudPlatform#7053

Note: It's a good idea to open an issue first for discussion.

## Checklist
- [x] I have followed [Sample Guidelines from AUTHORING_GUIDE.MD](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md)
- [ ] README is updated to include [all relevant information](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#readme-file)
- [x] **Tests** pass:   `nox -s py-3.6` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [x] **Lint** pass:   `nox -s lint` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [ ] These samples need a new **API enabled** in testing projects to pass (let us know which ones)
- [ ] These samples need a new/updated **env vars** in testing projects set to pass (let us know which ones)
- [x] Please **merge** this PR for me once it is approved.
- [ ] This sample adds a new sample directory, and I updated the [CODEOWNERS file](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/.github/CODEOWNERS) with the codeowners for this sample

Author: leahecole

composer/airflow_1_samples/constraints.txt

@@ -1,2 +1,3 @@
 pandas-gbq==0.14.1 # must be under 0.15.0 until https://github.com/apache/airflow/issues/15113 is addressed
 SQLAlchemy==1.3.23 # must be under 1.4 until at least Airflow 2.0 (check airflow setup.py for restrictions)
+WTForms==2.3.3 # Must stay under 3.0 because of https://github.com/dpgaspar/Flask-AppBuilder/issues/1732

composer/airflow_1_samples/noxfile_config.py

@@ -31,7 +31,7 @@
 TEST_CONFIG_OVERRIDE = {
     # You can opt out from the test for specific Python versions.
     # Skipping for Python 3.9 due to numpy compilation failure.
-    "ignored_versions": ["2.7", "3.9"],
+    "ignored_versions": ["2.7", "3.9", "3.10"],
     # Old samples are opted out of enforcing Python type hints
     # All new samples should feature them
     "enforce_type_hints": False,

composer/blog/gcp-tech-blog/unit-test-dags-cloud-build/constraints.txt

@@ -1 +1,2 @@
 SQLAlchemy==1.3.23 # must be under 1.4 until at least Airflow 2.0 (check airflow setup.py for restrictions)
+WTForms==2.3.3 # Must stay under 3.0 because of https://github.com/dpgaspar/Flask-AppBuilder/issues/1732