ci: use latest version of staticcheck instead of v0.1.2

A new version that fixes a false positive is out (v0.1.3). In order to
not have to bump the version manually, simply use latest.

Signed-off-by: Robin Hahling <robin.hahling@gw-computing.net>

.github/workflows/tests.yml

@@ -33,7 +33,7 @@ jobs:
     - name: Install and run staticcheck
       if: matrix.go-version >= '1.16'
       run: |
-        go install honnef.co/go/tools/cmd/staticcheck@v0.1.2
+        go install honnef.co/go/tools/cmd/staticcheck@latest
         staticcheck -version
         staticcheck -- ./...
     - name: Run unit tests