fix(ci): pass --shard to vitest in the windows e2e matrix [RED-738] (#1415)

The `e2e - checkly - windows` job declares a 4-way shard matrix, but all
four shards ran the entire 27-file e2e suite.

pnpm forwards a literal `--` verbatim into the script (npm strips it),
where vitest's parser collects everything after it into an argument list
it never reads — silently discarding --shard. Dropping the separator is
sufficient: pnpm appends trailing args to the script command as-is, so
--shard reaches vitest without one.

The compound `test:e2e` script is not the cause. Args appended to `A && B`
land at the end of B, and B is the vitest invocation.

Verified locally that the four shards now partition the suite 7/7/7/6 into
27 unique files. A green run is not evidence on its own — the broken form
passed too, running the full suite four times over.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: sorccu

.github/workflows/test.yml

@@ -174,7 +174,15 @@ jobs:
           cache: "pnpm"
       - run: pnpm install --frozen-lockfile
       - run: pnpm run prepack
-      - run: pnpm --filter checkly run test:e2e -- --shard=${{ matrix.shard }}
+      # Deliberately no `--` separator: pnpm appends trailing args to the
+      # script command as-is, so --shard reaches vitest without one. Unlike
+      # npm, pnpm forwards a literal `--` verbatim into the script, where
+      # vitest's parser collects everything after it into an argument list it
+      # never reads — silently discarding --shard. The suite still passes when
+      # that happens, so a green run is not evidence the flag landed; check
+      # that each shard reports fewer test files than the full suite and that
+      # the four counts sum to it.
+      - run: pnpm --filter checkly run test:e2e --shard=${{ matrix.shard }}
         env:
           CHECKLY_ACCOUNT_NAME: ${{ secrets.E2E_CHECKLY_ACCOUNT_NAME }}
           CHECKLY_ACCOUNT_ID: ${{ secrets.E2E_CHECKLY_ACCOUNT_ID }}