diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 66e300d..d932b39 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -10,7 +10,7 @@ on:
 jobs:
   build_sdist:
     name: Build sdist
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
 
@@ -37,7 +37,7 @@ jobs:
 
   build_generic_wheel:
     name: Build generic wheel (without speedups)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     env:
       # Build a wheel without speedups that can run on pure Python
       GENSHI_BUILD_SPEEDUP: 0
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index a25af71..2037fa0 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -4,10 +4,10 @@ on: [push, pull_request]
 
 jobs:
   tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: [2.7, 3.6, 3.7, 3.8, 3.9, "3.10", "3.11-dev", pypy2, pypy3]
+        python-version: [3.6, 3.7, 3.8, 3.9, "3.10", "3.11", pypy2, pypy3]
 
     steps:
       - uses: actions/checkout@v2
diff --git a/genshi/compat.py b/genshi/compat.py
index 2f8c481..2abca13 100644
--- a/genshi/compat.py
+++ b/genshi/compat.py
@@ -20,6 +20,7 @@
 except ImportError:
     import _ast as ast
 import sys
+import warnings
 from types import CodeType
 
 import six
@@ -137,13 +138,15 @@ def build_code_chunk(code, filename, name, lineno):
 
 # In Python 3.8, Str and Ellipsis was replaced by Constant
 
-try:
-    _ast_Ellipsis = ast.Ellipsis
-    _ast_Str = ast.Str
-    _ast_Str_value = lambda obj: obj.s
-except AttributeError:
-    _ast_Ellipsis = _ast_Str = ast.Constant
-    _ast_Str_value = lambda obj: obj.value
+with warnings.catch_warnings():
+    warnings.filterwarnings('error', category=DeprecationWarning)
+    try:
+        _ast_Ellipsis = ast.Ellipsis
+        _ast_Str = ast.Str
+        _ast_Str_value = lambda obj: obj.s
+    except (AttributeError, DeprecationWarning):
+        _ast_Ellipsis = _ast_Str = ast.Constant
+        _ast_Str_value = lambda obj: obj.value
 
 class _DummyASTItem(object):
     pass