Use PostgreSQL matrix

Signed-off-by: Hiroshi Hatake <[email protected]>

Author: cosmo0920

.github/workflows/linux.yml

@@ -10,11 +10,12 @@ jobs:
       fail-fast: false
       matrix:
         ruby: [ '2.4', '2.5', '2.6', '2.7' ]
+        postgres: [ '9', '10', '11', '12', '13' ]
         os:
           - ubuntu-latest
     services:
       postgres:
-        image: postgres:13
+        image: postgres:${{ matrix.postgres }}
         ports:
           - 5432:5432
         env:
@@ -26,7 +27,7 @@ jobs:
           --health-interval 10s
           --health-timeout 5s
           --health-retries 5
-    name: Ruby ${{ matrix.ruby }} unit testing on ${{ matrix.os }}
+    name: Ruby ${{ matrix.ruby }} with PostgreSQL ${{ matrix.postgres }} unit testing on ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2
     - uses: ruby/setup-ruby@v1