CI: skip regular `go test` on linux

See the added comment.
An alternative would be to split up the work into more jobs,
but that doesn't feel necessary, and we still have a global limit
on how many free runners we can run jobs on at once.

While here, update the comments, and remove unnecessary step names.

.github/workflows/test.yml

@@ -35,21 +35,24 @@ jobs:
       with:
         go-version: ${{ matrix.go-version }}
         cache: false
-    - name: Test
+    # linux already runs the tests with -race below, plus extra checks,
+    # so skip the regular tests to prevent it from taking the longest.
+    - if: matrix.os != 'ubuntu-latest'
       run: go test -timeout=15m ./...
+    # macos and windows failures with bincmp can be hard to reproduce locally,
+    # so upload the binaries as artifacts.
     - uses: actions/upload-artifact@v3
       if: failure()
       with:
         name: bincmp_output
         path: bincmp_output/
-    - name: Test with -race
-      # macos and windows tend to be a bit slower,
-      # and it's rare that a race in garble would be OS-specific.
-      if: matrix.os == 'ubuntu-latest'
+    # macos and windows tend to be a bit slower,
+    # and it's rare that a race in garble would be OS-specific.
+    - if: matrix.os == 'ubuntu-latest'
       run: go test -race -timeout=20m ./...
 
     # Static checks from this point forward. Only run on one Go version and on
-    # Linux, since it's the fastest platform, and the tools behave the same.
+    # linux, since it's the fastest platform, and the tools behave the same.
     - name: Test third-party project builds
       if: matrix.os == 'ubuntu-latest' && matrix.go-version == '1.20.x'
       run: |