ci: drop windows-latest from typecheck matrix (#1747)

* ci: drop windows-latest from typecheck matrix

tsc is OS-agnostic; the windows-latest run duplicates the ubuntu pass
and adds ~5 min of CI time per push. Real Windows regressions surface
in the unit/web test matrix, which still runs on both OSes.

* ci: collapse typecheck matrix to a plain ubuntu-latest job

With windows-latest dropped, the single-OS matrix was just indirection
and produced a noisy 'Typecheck (ubuntu-latest)' job name. Use a direct
runs-on instead.

.github/workflows/ci.yml

@@ -30,12 +30,8 @@ jobs:
       - run: pnpm lint
 
   typecheck:
-    name: Typecheck (${{ matrix.os }})
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-latest, windows-latest]
-    runs-on: ${{ matrix.os }}
+    name: Typecheck
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - uses: pnpm/action-setup@v4