simplify sharding in package tests for CI; increase to 12 shards (#4158)

* simplify sharding in package tests for CI; increase to 12 shards

Signed-off-by: Avi Deitcher <avi@deitcher.net>

* for CI setup-go action, determine it based on go.mod file

Signed-off-by: Avi Deitcher <avi@deitcher.net>

---------

Signed-off-by: Avi Deitcher <avi@deitcher.net>

.github/workflows/package_release.yml

@@ -9,13 +9,13 @@ jobs:
     if: github.ref_type == 'tag' && startsWith(github.ref, 'refs/tags/pkg-v')
     runs-on: ubuntu-latest
     steps:
-    - name: Set up Go 1.22
-      uses: actions/setup-go@v5
-      with:
-        go-version: 1.22.3
-      id: go
     - name: Check out code
       uses: actions/checkout@v4
+    - name: Set up Go based on go.mod
+      uses: actions/setup-go@v5
+      with:
+        go-version-file: 'src/cmd/linuxkit/go.mod'
+      id: go
     - name: Ensure bin/ directory
       run: mkdir -p bin
     - name: Install linuxkit