fix: Removing Python 3.8 support due to EOL

PiperOrigin-RevId: 752361448

Author: sararob

.github/sync-repo-settings.yaml

@@ -16,7 +16,6 @@ branchProtectionRules:
  - 'cla/google'
  - 'Kokoro docs-presubmit'
  - 'Presubmit - Lint and Coverage'
- - 'Presubmit - Unit Tests Python 3.8'
  - 'Presubmit - Unit Tests Python 3.9'
  - 'Presubmit - Unit Tests Python 3.10'
  - 'Presubmit - Unit Tests Python 3.11'

.kokoro/docker/docs/Dockerfile

@@ -80,4 +80,4 @@ RUN wget -O /tmp/get-pip.py 'https://bootstrap.pypa.io/get-pip.py' \
 # Test pip
 RUN python3 -m pip
 
-CMD ["python3.8"]
+CMD ["python3.9"]

.kokoro/presubmit/presubmit.cfg

@@ -1,11 +1,11 @@
 # Format: //devtools/kokoro/config/proto/build.proto
 
 # Run all sessions except system tests and docs builds
-# This only runs unit tests for Python 3.8 since unit tests are required for `cover` to run
+# This only runs unit tests for Python 3.9 since unit tests are required for `cover` to run
 # Other Python version unit tests are run separately
 env_vars: {
  key: "NOX_SESSION"
- value: "unit-3.8 lint lint_setup_py blacken cover"
+ value: "unit-3.9 lint lint_setup_py blacken cover"
 }
 
 # Run unit tests in parallel, splitting up by file

.kokoro/presubmit/release.cfg

@@ -3,7 +3,7 @@
 # Run system tests in presubmit for library releases
 env_vars: {
  key: "NOX_SESSION"
- value: "system-3.8 unit"
+ value: "system-3.9 unit"
 }
 
 # Run system tests in parallel, splitting up by file