GitHub: fix permission denied in lint CI step

This attempts to fix the following error that sometimes occurs on the
GitHub runners:

 go: github.com/lightninglabs/lightning-terminal imports
	github.com/lightningnetwork/lnd/kvdb imports
	github.com/lightningnetwork/lnd/kvdb/etcd imports
	go.etcd.io/etcd/server/v3/embed: mkdir /home/runner/go/pkg/mod/cache/download/go.etcd.io/etcd/server: permission denied

The suspicion is that the lint step that runs as root within docker
changes the permissions of some of the module cache directories.
So by simply changing the order of operations, this should be fixed.

Author: guggero

.github/workflows/main.yml

@@ -207,7 +207,7 @@ jobs:
         run: mkdir -p app/build; touch app/build/index.html
 
       - name: run check
-        run: make lint mod-check
+        run: make mod-check && make lint
 
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   # unit tests