See if we can get away with using another version of clang with coverity

.gitlab-ci.yml

@@ -67,23 +67,23 @@ Coverity:
   tags:
     - docker
     - linux
-  image: ubuntu:22.04
+  image: ubuntu:20.04
   stage: build
   rules:
     - if: $CI_PIPELINE_SOURCE == "schedule"
   cache:
-    key: Coverity.ubuntu_22.04.v1
+    key: Coverity.ubuntu_20.04.v1
     paths:
     - apt-cache/
     - ccache/
   variables:
     CCACHE_SIZE: 2G
-    CC: clang
-    CXX: clang++
+    CC: clang-11
+    CXX: clang++-11
     CMAKE_BUILD_TYPE: Debug
     CMAKE_CXX_FLAGS_DEBUG: -O0
   before_script:
-    - CI/install_debian_deps.sh clang openmw-deps openmw-deps-dynamic
+    - CI/install_debian_deps.sh coverity openmw-deps openmw-deps-dynamic
     - curl -o /tmp/cov-analysis-linux64.tgz https://scan.coverity.com/download/linux64
       --form project=$COVERITY_SCAN_PROJECT_NAME --form token=$COVERITY_SCAN_TOKEN
     - tar xfz /tmp/cov-analysis-linux64.tgz

CI/install_debian_deps.sh

@@ -11,6 +11,7 @@ print_help() {
 declare -rA GROUPED_DEPS=(
   [gcc]="binutils gcc build-essential cmake ccache curl unzip git pkg-config mold"
   [clang]="binutils clang make cmake ccache curl unzip git pkg-config mold"
+  [coverity]="binutils clang-11 make cmake ccache curl unzip git pkg-config"
 
   # Common dependencies for building OpenMW.
   [openmw-deps]="