CI: Remove ubuntu 18.04

ubuntu 18.04 is replaced with ubuntu 20.04.

Signed-off-by: Juergen Repp <[email protected]>

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
  if: "!contains(github.ref, 'coverity_scan')"
  strategy:
  matrix:
- docker_image: [ubuntu-18.04, ubuntu-20.04, fedora-30, opensuse-leap, fedora-32, ubuntu-22.04]
+ docker_image: [ubuntu-20.04, fedora-30, opensuse-leap, fedora-32, ubuntu-22.04]
  compiler: [gcc, clang]
  steps:
  - name: Check out repository
@@ -55,7 +55,7 @@ jobs:
  with:
  PROJECT_NAME: ${{ github.event.repository.name }}
  ENABLE_COVERAGE: true
- DOCKER_IMAGE: ubuntu-18.04
+ DOCKER_IMAGE: ubuntu-20.04
  CC: gcc
  - name: failure cat build logs
  if: ${{ failure() }}
@@ -77,7 +77,7 @@ jobs:
  REPO_BRANCH: ${{ github.ref }}
  REPO_NAME: ${{ github.repository }}
  ENABLE_COVERITY: true
- DOCKER_IMAGE: ubuntu-18.04
+ DOCKER_IMAGE: ubuntu-20.04
  CC: gcc
  COVERITY_SCAN_TOKEN: ${{ secrets.COVERITY_SCAN_TOKEN }}
  COVERITY_SUBMISSION_EMAIL: [email protected]