Add static SDK CI workflow (#500)

Add static SDK CI workflow which runs on commits to PRs, merges to main
and daily on main.

Author: rnro

.github/workflows/main.yml

@@ -75,3 +75,7 @@ jobs:
     with:
       runner_pool: nightly
       build_scheme: swift-nio-http2-Package
+
+  static-sdk:
+    name: Static SDK
+    uses: apple/swift-nio/.github/workflows/static_sdk.yml@main

.github/workflows/pull_request.yml

@@ -79,3 +79,7 @@ jobs:
     with:
       runner_pool: general
       build_scheme: swift-nio-http2-Package
+
+  static-sdk:
+    name: Static SDK
+    uses: apple/swift-nio/.github/workflows/static_sdk.yml@main