[ci] Fix build image job.

scripts/ci/extends/template-build-linux.yml

@@ -15,6 +15,7 @@
     - git lfs checkout
     - mkdir -p $BUILD_DIR
     - cd $BUILD_DIR
+    - \[ "${CONAN_USER_HOME}" == "${CI_PROJECT_DIR}/.conan" \] && conan remove --system-reqs '*'
 
   script:
     - >

scripts/ci/jobs/build-gui-linux.yml

@@ -16,6 +16,7 @@ build gui linux:
 
   variables:
     BUILD_DIR: "build-gui-linux"
+    CONAN_USER_HOME: "$CI_PROJECT_DIR/.conan"
     CMAKE_ARGS: >-
       -DOGS_USE_CONAN=ON
       -DOGS_USE_PCH=OFF
@@ -25,3 +26,8 @@ build gui linux:
 
   image:
     name: $CONTAINER_GCC_GUI_IMAGE
+
+  cache:
+    paths:
+      - $CCACHE_DIR
+      - $CONAN_USER_HOME

scripts/ci/jobs/build-linux-petsc.yml

 build linux petsc:
   extends: .template-build-linux
   tags:
-    - envinf1
-    - docker-shell
+    - envinf1-shell
 
   variables:
     BUILD_DIR: "build-petsc"

scripts/ci/jobs/build_image.yml

@@ -4,10 +4,11 @@ build container images:
     - changes:
       - ThirdParty/container-maker
       - scripts/ci/jobs/build_image.yml
+      when: always
     - if: '$CI_COMMIT_BRANCH == "master"'
       when: always
   tags:
-    - docker-shell
+    - envinf1-shell # can be changed back when instance-level vars are implemented
 
   variables:
     GIT_LFS_SKIP_SMUDGE: "1"