github/workflows: set configuration in matrix

Create a special configuration for each matrix build.
Allows programmatic access to the build directory
since the configuration name is constant for each run.
No wildcards needed.

.github/workflows/lone.yml

@@ -41,6 +41,7 @@ jobs:
               LDFLAGS: -Wl,--spare-program-headers,2
 
     env:
+      CONFIGURATION: ${{ matrix.compiler.name }}-${{ matrix.linker.name }}
       CC: ${{ matrix.compiler.env.CC }}
       LD: ${{ matrix.linker.env.LD }}
       CFLAGS: ${{ matrix.compiler.env.CFLAGS }}