Drop RBS 3.2 test and add RBS 3.3 and 3.8 test

RBS 3.1.x and 3.2.x depends on abbrev but abbrev was not added to runtime dependency.
Abbrev is not a default gem in Ruby 3.4.

Author: tompng

.github/workflows/test.yml

@@ -35,7 +35,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rbs: ['latest', '3.6', '3.4', '3.2', '3.0', '2.7.0']
+        rbs: ['latest', '3.8', '3.6', '3.4', '3.3', '3.0', '2.7.0']
     env:
       GEMFILE_RBS_VERSION: ${{ matrix.rbs }}
     steps: