Add back ruby 1.9 exclusions

Author: Matt Muller

.github/workflows/ci.yml

@@ -18,6 +18,10 @@ jobs:
         ruby: [1.9, '2.0', 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3, 3.4, jruby-9.1, jruby-9.2, jruby-9.3, jruby-9.4]
         gemfile: [no-deps, json-latest, json-old, json-pure]
         exclude:
+          - ruby: 1.9
+            gemfile: json-latest
+          - ruby: 1.9
+            gemfile: json-pure
           - ruby: '3.0'
             gemfile: json-old
           - ruby: 3.1