ci: install gmock in the Fedora 31 image

The gmock libraries are referenced by GTest's CMake package files.

While at it, also explicitly install gettext.  It is installed already,
but make it explicit for future testing of the FindGettext module.

.gitlab/ci/docker/fedora31/install_deps.sh

@@ -39,8 +39,10 @@ dnf install --setopt=install_weak_deps=False -y \
     fontconfig-devel \
     freetype-devel \
     gdal-devel \
+    gettext \
     giflib-devel \
     glew-devel \
+    gmock \
     gnutls-devel \
     gsl-devel \
     gtest-devel \

.gitlab/os-linux.yml

@@ -49,7 +49,7 @@
 ### Fedora
 
 .fedora31:
-    image: "kitware/cmake:ci-fedora31-x86_64-2020-10-20"
+    image: "kitware/cmake:ci-fedora31-x86_64-2020-10-22"
 
     variables:
         GIT_CLONE_PATH: "$CI_BUILDS_DIR/cmake ci/long file name for testing purposes"