add target openbsd-7.8

Author: leleliu008

.github/workflows/cross-compile-for-openbsd-on-ubuntu.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        openbsd-release-version: ['7.7']
+        openbsd-release-version: ['7.8', '7.7']
         # https://cdn.openbsd.org/pub/OpenBSD/
 
     runs-on: ubuntu-latest