ci: enable synctest on Go 1.24

Author: marten-seemann

.github/workflows/test.yml

@@ -10,6 +10,8 @@ jobs:
     runs-on: ${{ matrix.os }}-latest
     name: Tests (${{ matrix.os}}, Go ${{ matrix.go }})
     timeout-minutes: 10
+    env:
+      GOEXPERIMENT: ${{ matrix.go == '1.24.x' && 'synctest' || '' }}
     steps:
       - uses: actions/checkout@v5
       - uses: actions/setup-go@v6