Merge pull request OSGeo#9199 from rouault/ci_ubuntugis_unstable

CI: revert to previous method to add ppa:ubuntugis/ubuntugis-unstable

.github/workflows/cmake_builds.yml

@@ -43,10 +43,7 @@ jobs:
             ${{ runner.os }}-${{ env.cache-name }}
     - name: Install dependency
       run: |
-        # This currently fails as of https://lists.osgeo.org/pipermail/ubuntu/2023-October/002046.html
-        # sudo add-apt-repository -y ppa:ubuntugis/ubuntugis-unstable
-        sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6B827C12C2D425E227EDCA75089EBE08314DF160
-        sudo add-apt-repository -y http://ppa.launchpad.net/ubuntugis/ubuntugis-unstable/ubuntu/
+        sudo add-apt-repository -y ppa:ubuntugis/ubuntugis-unstable
         sudo apt-get update
         sudo apt-get install -y -q bison libaec-dev libjpeg-dev libgif-dev liblzma-dev libzstd-dev libgeos-dev git \
            libcurl4-gnutls-dev libproj-dev libxml2-dev  libxerces-c-dev libnetcdf-dev netcdf-bin \