Test GNUStep libobjc2 v1.8 as well

Author: madsmtm

.github/workflows/ci.yml

@@ -74,6 +74,11 @@ jobs:
             test-args: --no-run
             # Newest SDK that supports 32-bit
             sdk: "10.13"
+          - name: Test GNUStep with libobjc2 v1.8
+            os: ubuntu-latest
+            target: x86_64-unknown-linux-gnu
+            runtime: gnustep-1-8
+            libobjc2: "1.8"
           - name: Test GNUStep with libobjc2 v1.9
             os: ubuntu-latest
             target: x86_64-unknown-linux-gnu