GitHub Actions: use python 3.10 instead of 3.11 on MacOS

See https://github.com/actions/runner-images/issues/6817

.github/workflows/testing-mac.yml

@@ -26,8 +26,8 @@ jobs:
       run: brew update
     - name: install tools and libraries
       run: |
-        # python@3.11 symlink 2to3-3.11 to /usr/local/bin/2to3-3.11, but it already exists. so we need use --overwrite option when installing python@3.11, python@3.11 is depended by gdb.
-        brew install --overwrite python@3.11
+        # See https://github.com/actions/runner-images/issues/6817.
+        brew install --overwrite python@3.10
         brew install automake pkg-config bash libxml2 jansson libyaml gdb docutils pcre2
     - name: autogen.sh
       run: ./autogen.sh