build: Drop testing on older Ruby and Mongo versions.

We moved on from these old versions of Ruby and Mongo 2 releases ago but
didn't come back to clean this up.  Now the 3.0.4 tests are failing and
it's not really valuable to fix them since we should have already
dropped that support a while ago.

.github/workflows/ci.yml

@@ -13,18 +13,15 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['3.0.4', '3.1.4', '3.3.0']
-        mongodb-version: ['4.2.14', '6', '7']
+        ruby-version: ['3.1.4', '3.3.0']
+        mongodb-version: ['7']
         include:
-          - ruby-version: '3.0.4'
-            gemfile: Gemfile3
-            allow-failure: false
           - ruby-version: '3.1.4'
             gemfile: Gemfile
-            allow-failure: true
+            allow-failure: false
           - ruby-version: '3.3.0'
             gemfile: Gemfile
-            allow-failure: true
+            allow-failure: false
 
     env:
       SEARCH_SERVER_ES7: http://localhost:9200