ci: update DOCKER_APT_PKG_VER to 5:29.2.1-1~ubuntu.24.04~noble

The GitHub Actions runner now has Docker 5:29.1.5 pre-installed, making
the previously pinned version (5:28.3.3) a downgrade, which caused all
CI jobs to fail with "Packages were downgraded and -y was used without
--allow-downgrades". Bump the pin to the current candidate 5:29.2.1.

Author: ImreSamu

.github/workflows/main.yml

@@ -67,7 +67,7 @@ jobs:
     env:
       VERSION: ${{ matrix.postgres }}-${{ matrix.postgis }}
       VARIANT: ${{ matrix.variant }}
-      DOCKER_APT_PKG_VER: '5:28.3.3-1~ubuntu.24.04~noble'
+      DOCKER_APT_PKG_VER: '5:29.2.1-1~ubuntu.24.04~noble'
 
     steps:
     - name: Install/config specific version of Docker packages