Fix itk install error when python=3.8 (#7719)

Fixes #7716

set python 3.9 for pythonapp.yml

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [ ] New tests added to cover the changes.
- [ ] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [ ] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [ ] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

---------

Signed-off-by: YunLiu <55491388+KumoLiu@users.noreply.github.com>

Author: KumoLiu

.github/workflows/pythonapp.yml

@@ -70,10 +70,10 @@ jobs:
         maximum-size: 16GB
         disk-root: "D:"
     - uses: actions/checkout@v4
-    - name: Set up Python 3.8
+    - name: Set up Python 3.9
       uses: actions/setup-python@v5
       with:
-        python-version: '3.8'
+        python-version: '3.9'
     - name: Prepare pip wheel
       run: |
         which python

tests/test_clip_intensity_percentilesd.py

@@ -96,7 +96,7 @@ def test_channel_wise(self, p):
         for i, c in enumerate(im):
             lower, upper = percentile(c, (5, 95))
             expected = clip(c, lower, upper)
-            assert_allclose(result[key][i], p(expected), type_test="tensor", rtol=1e-4, atol=0)
+            assert_allclose(result[key][i], p(expected), type_test="tensor", rtol=1e-3, atol=0)
 
     def test_ill_sharpness_factor(self):
         key = "img"