coverity-scan.yml: fix

.github/workflows/coverity-scan.yml

@@ -12,7 +12,7 @@ on:
 # A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     if: github.repository == 'MapServer/MapServer'
     steps:
       - uses: actions/checkout@v2
@@ -21,7 +21,7 @@ jobs:
         run: |
           sudo add-apt-repository -y ppa:ubuntugis/ubuntugis-unstable
           sudo apt-get update
-          sudo apt-get install --allow-unauthenticated protobuf-c-compiler libprotobuf-c-dev bison flex libfribidi-dev cmake librsvg2-dev colordiff libpq-dev libpng-dev libjpeg-dev libgif-dev libgeos-dev libfreetype6-dev libfcgi-dev libcurl4-gnutls-dev libcairo2-dev libgdal-dev libproj-dev libxml2-dev libexempi-dev lcov lftp postgis libharfbuzz-dev gdal-bin ccache curl postgresql-server-dev-10 postgresql-10-postgis-3 postgresql-10-postgis-3-scripts swig
+          sudo apt-get install --allow-unauthenticated protobuf-c-compiler libprotobuf-c-dev bison flex libfribidi-dev cmake librsvg2-dev colordiff libpq-dev libpng-dev libjpeg-dev libgif-dev libgeos-dev libfreetype6-dev libfcgi-dev libcurl4-gnutls-dev libcairo2-dev libgdal-dev libproj-dev libxml2-dev libexempi-dev lcov lftp postgis libharfbuzz-dev gdal-bin ccache curl postgresql-server-dev-12 postgresql-12-postgis-3 postgresql-12-postgis-3-scripts swig
       - name: Build MapServer
         run: |
           mkdir build