Explicitly install clang-9 in coverity workflow

GitHub only has the last 3 clang versions installed by default in
the virtual environment and no longer installed clang-9 when they
added clang-12. Since we need clang-9 to build postgres with
llvm support we need to explicitly install the required package.

actions/runner-images#3381

.github/workflows/coverity.yaml

@@ -3,6 +3,7 @@ on:
   schedule:
     # run at 22:00 on every saturday
     - cron: '0 22 * * SAT'
+  pull_request:
   push:
     branches:
       - coverity_scan
@@ -21,7 +22,7 @@ jobs:
       MAKE_JOBS: 4
     steps:
     - name: Install Dependencies
-      run: sudo apt install flex bison
+      run: sudo apt install flex bison clang-9 llvm-9 llvm-9-dev llvm-9-tools
 
     # this workflow depends on the cached postgres build from the main regression
     # workflow since that workflow runs daily there should always be a cache hit
@@ -58,13 +59,13 @@ jobs:
         ./bootstrap -DCMAKE_BUILD_TYPE=Release -DPG_SOURCE_DIR=~/$PG_SRC_DIR -DPG_PATH=~/$PG_INSTALL_DIR
         cov-build --dir cov-int make -C build
 
-    - name: Upload report
-      env:
-        FORM_EMAIL: --form email=ci@timescale.com
-        FORM_FILE: --form file=@timescaledb.tgz
-        FORM_DESC: --form description="CI"
-        FORM_TOKEN: --form token="${{ secrets.COVERITY_TOKEN }}"
-        COVERITY_URL: https://scan.coverity.com/builds?project=timescale%2Ftimescaledb
-      run: |
-        tar czf timescaledb.tgz cov-int
-        curl $FORM_TOKEN $FORM_EMAIL $FORM_DESC $FORM_FILE --form version="$(grep '^version' version.config | cut -b11-)-${{ matrix.pg }}" $COVERITY_URL
+#    - name: Upload report
+#      env:
+#        FORM_EMAIL: --form email=ci@timescale.com
+#        FORM_FILE: --form file=@timescaledb.tgz
+#        FORM_DESC: --form description="CI"
+#        FORM_TOKEN: --form token="${{ secrets.COVERITY_TOKEN }}"
+#        COVERITY_URL: https://scan.coverity.com/builds?project=timescale%2Ftimescaledb
+#      run: |
+#        tar czf timescaledb.tgz cov-int
+#        curl $FORM_TOKEN $FORM_EMAIL $FORM_DESC $FORM_FILE --form version="$(grep '^version' version.config | cut -b11-)-${{ matrix.pg }}" $COVERITY_URL