[buildbot] ci: use Python 3.11 from Debian 12 for testing

[LEDE Commits]

ynezz pushed a commit to buildbot.git, branch main:
https://git.openwrt.org/339e00d8f1cd1a5d9824056af5776175e7e9ea32

commit 339e00d8f1cd1a5d9824056af5776175e7e9ea32
Author: Petr Štetiar <ynezz at true.cz>
AuthorDate: Sat Sep 28 07:14:12 2024 +0000

    ci: use Python 3.11 from Debian 12 for testing
    
    In commit 3ac7d39bd4c3 ("buildworker,buildmaster: bump Debian to version
    12") we switched the base system to Debian 12 which uses Python 3.11.2,
    thus lets test on CI with same version.
    
    Signed-off-by: Petr Štetiar <ynezz at true.cz>
---
 .github/workflows/build-push.yml | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/.github/workflows/build-push.yml b/.github/workflows/build-push.yml
index 7d8f985..e3c0be6 100644
--- a/.github/workflows/build-push.yml
+++ b/.github/workflows/build-push.yml
@@ -23,8 +23,7 @@ jobs:
     strategy:
       matrix:
         python-version:
-          - "3.9"
-          - "3.10"
+          - "3.11"
 
     steps:
       - name: Checkout