drop Python 3.8 support (#10265)

* drop Python 3.8

Note that this PR only makes typing related changes.
Other changes can be done once this gets merged, they
are relatively few in numbers.

* bump build python version

* add typing_extensions to lint group

.github/workflows/build.yaml

@@ -25,7 +25,7 @@ jobs:
 
     - uses: actions/setup-python@v5
       with:
-        python-version: 3.8
+        python-version: 3.12
 
     - run: python -m pip install --upgrade pip setuptools_scm build twine
 

.github/workflows/tests.yaml

@@ -23,7 +23,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04, windows-latest, macos-latest]
-        pyv: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        pyv: ["3.9", "3.10", "3.11", "3.12"]
 
     steps:
     - uses: actions/checkout@v4