ci: give a name to a step

Otherwise it's displayed using the first line of the run: argument, i.e.
like this:

> Run # This corresponds with the list in Makefile:1, but omits the "userns"

which is a bit confusing.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

.github/workflows/test.yml

@@ -17,7 +17,8 @@ jobs:
         cache-dependency-path: ${{ steps.gosum.outputs.stdout }}
     - name: Checkout code
       uses: actions/checkout@v4
-    - if: ${{ matrix.go-version == '1.18.x' }}
+    - name: Set PACKAGES env
+      if: ${{ matrix.go-version == '1.18.x' }}
       run: |
         # This corresponds with the list in Makefile:1, but omits the "userns"
         # and "capability" modules, which require go1.21 as minimum.