flake.nix: exclude armv6-linux and riscv64-linux from checks

Otherwise, `nix flake check --all-systems --json` fails with:

    error:
           … while calling the 'head' builtin
             at /nix/store/0jy5khqx0rfw8avcq6z5zaxaj2ppz8d3-source/lib/attrsets.nix:1575:11:
             1574|         || pred here (elemAt values 1) (head values) then
             1575|           head values
                 |           ^
             1576|         else

           … while evaluating the attribute 'value'
             at /nix/store/0jy5khqx0rfw8avcq6z5zaxaj2ppz8d3-source/lib/modules.nix:816:9:
              815|     in warnDeprecation opt //
              816|       { value = addErrorContext "while evaluating the option `${showOption loc}':" value;
                 |         ^
              817|         inherit (res.defsFinal') highestPrio;

           … while evaluating the option `system.build.toplevel':

           … while evaluating definitions from `/nix/store/0jy5khqx0rfw8avcq6z5zaxaj2ppz8d3-source/nixos/modules/system/activation/top-level.nix':

           … while evaluating the option `system.systemBuilderArgs':

           … while evaluating definitions from `/nix/store/0jy5khqx0rfw8avcq6z5zaxaj2ppz8d3-source/nixos/modules/system/activation/activatable-system.nix':

           … while evaluating the option `system.activationScripts.etc.text':

           … while evaluating definitions from `/nix/store/0jy5khqx0rfw8avcq6z5zaxaj2ppz8d3-source/nixos/modules/system/etc/etc-activation.nix':

           … while evaluating definitions from `/nix/store/0jy5khqx0rfw8avcq6z5zaxaj2ppz8d3-source/nixos/modules/system/etc/etc.nix':

           … while evaluating the option `environment.etc.dbus-1.source':

           (stack trace truncated; use '--show-trace' to show the full, detailed trace)

           error: cannot bootstrap GHC on this platform ('riscv64-linux' with libc 'defaultLibc')

flake.nix

@@ -80,8 +80,17 @@
 
       checks = forAllSystems (system: {
         tarball = jobs.${system}.tarball;
-        # Exclude power64 due to "libressl is not available on the requested hostPlatform" with hostPlatform being power64
-      } // lib.optionalAttrs (self.legacyPackages.${system}.stdenv.hostPlatform.isLinux && !self.legacyPackages.${system}.targetPlatform.isPower64) {
+      } // lib.optionalAttrs
+        (
+          self.legacyPackages.${system}.stdenv.hostPlatform.isLinux
+          # Exclude power64 due to "libressl is not available on the requested hostPlatform" with hostPlatform being power64
+          && !self.legacyPackages.${system}.targetPlatform.isPower64
+          # Exclude armv6l-linux due to "cannot bootstrap GHC on this platform ('armv6l-linux' with libc 'defaultLibc')"
+          && system != "armv6l-linux"
+          # Exclude riscv64-linux due to "cannot bootstrap GHC on this platform ('riscv64-linux' with libc 'defaultLibc')"
+          && system != "riscv64-linux"
+        )
+      {
         # Test that ensures that the nixosSystem function can accept a lib argument
         # Note: prefer not to extend or modify `lib`, especially if you want to share reusable modules
         #       alternatives include: `import` a file, or put a custom library in an option or in `_module.args.<libname>`