Remove support for python 3.8 (#17908)

### Pull Request Checklist

<!-- Please read
https://element-hq.github.io/synapse/latest/development/contributing_guide.html
before submitting your pull request -->

* [X] Pull request is based on the develop branch
* [X] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
  - Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [X] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct
(run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

---------

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

.github/workflows/latest_deps.yml

@@ -132,9 +132,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - sytest-tag: focal
+          - sytest-tag: bullseye
 
-          - sytest-tag: focal
+          - sytest-tag: bullseye
             postgres: postgres
             workers: workers
             redis: redis

.github/workflows/release-artifacts.yml

@@ -102,7 +102,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04, macos-12]
+        os: [ubuntu-22.04, macos-12]
         arch: [x86_64, aarch64]
         # is_pr is a flag used to exclude certain jobs from the matrix on PRs.
         # It is not read by the rest of the workflow.
@@ -144,7 +144,7 @@ jobs:
 
       - name: Only build a single wheel on PR
         if: startsWith(github.ref, 'refs/pull/')
-        run: echo "CIBW_BUILD="cp38-manylinux_${{ matrix.arch }}"" >> $GITHUB_ENV
+        run: echo "CIBW_BUILD="cp39-manylinux_${{ matrix.arch }}"" >> $GITHUB_ENV
 
       - name: Build wheels
         run: python -m cibuildwheel --output-dir wheelhouse

.github/workflows/tests.yml

@@ -397,7 +397,7 @@ jobs:
     needs:
       - linting-done
       - changes
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
 
@@ -409,12 +409,12 @@ jobs:
       # their build dependencies
       - run: |
           sudo apt-get -qq update
-          sudo apt-get -qq install build-essential libffi-dev python-dev \
+          sudo apt-get -qq install build-essential libffi-dev python3-dev \
             libxml2-dev libxslt-dev xmlsec1 zlib1g-dev libjpeg-dev libwebp-dev
 
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.8'
+          python-version: '3.9'
 
       - name: Prepare old deps
         if: steps.cache-poetry-old-deps.outputs.cache-hit != 'true'
@@ -458,7 +458,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["pypy-3.8"]
+        python-version: ["pypy-3.9"]
         extras: ["all"]
 
     steps:
@@ -580,7 +580,7 @@ jobs:
     strategy:
       matrix:
         include:
-          - python-version: "3.8"
+          - python-version: "3.9"
             postgres-version: "11"
 
           - python-version: "3.11"

.github/workflows/twisted_trunk.yml

@@ -99,11 +99,11 @@ jobs:
     if: needs.check_repo.outputs.should_run_workflow == 'true'
     runs-on: ubuntu-latest
     container:
-      # We're using ubuntu:focal because it uses Python 3.8 which is our minimum supported Python version.
+      # We're using debian:bullseye because it uses Python 3.9 which is our minimum supported Python version.
       # This job is a canary to warn us about unreleased twisted changes that would cause problems for us if
       # they were to be released immediately. For simplicity's sake (and to save CI runners) we use the oldest
       # version, assuming that any incompatibilities on newer versions would also be present on the oldest.
-      image: matrixdotorg/sytest-synapse:focal
+      image: matrixdotorg/sytest-synapse:bullseye
       volumes:
         - ${{ github.workspace }}:/src