Enable release mode builds

### Motivation:

Some errors do not show up in debug builds. Enabling release mode builds improves the CI coverage.

### Modifications:

Enable release mode builds for pull requests and scheduled builds on main.

### Result:

Improved CI coverage.

Author: josephnoir

.github/workflows/main.yml

@@ -32,3 +32,7 @@ jobs:
     with:
       runner_pool: nightly
       build_scheme: swift-async-dns-resolver
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main

.github/workflows/pull_request.yml

@@ -37,3 +37,7 @@ jobs:
     with:
       runner_pool: general
       build_scheme: swift-async-dns-resolver
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main