GH-45381: [CI][Packaging][Conan] Use the latest supported image

Based on
https://github.com/conan-io/conan-docker-tools/blob/master/images/README.md#official-docker-images,
"gcc11-ubuntu16.04" is only supported image.

.env

@@ -101,5 +101,5 @@ PYTHON_WHEEL_WINDOWS_TEST_IMAGE_REVISION=2025-01-27
 # Use conanio/${CONAN_BASE}:{CONAN_VERSION} for "docker compose run --rm conan".
 # See https://github.com/conan-io/conan-docker-tools#readme and
 # https://hub.docker.com/u/conanio for available images.
-CONAN_BASE=gcc10
-CONAN_VERSION=1.62.0
+CONAN_BASE=gcc11-ubuntu16.04
+CONAN_VERSION=2.12.1

docker-compose.yml

@@ -742,8 +742,8 @@ services:
     # Usage:
     #   docker compose run --rm conan
     # Parameters:
-    #   CONAN_BASE: gcc11, gcc11-armv7, ...
-    #   CONAN_VERSION: 1.62.0
+    #   CONAN_BASE: gcc11-ubuntu16.04, ...
+    #   CONAN_VERSION: 2.12.1, ...
     #   See https://github.com/conan-io/conan-docker-tools#readme for
     #   available images.
     image: conanio/${CONAN_BASE}:${CONAN_VERSION}