ci: add indicate toolchain file in job name

Author: robjtede

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   install:
-    name: Rust ${{matrix.rust}} ${{matrix.os}}
+    name: Rust ${{matrix.rust || '(toolchain file)'}} ${{matrix.os}}
     runs-on: ${{matrix.os}}
     strategy:
       fail-fast: false