Enable release mode builds (#177)

### 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

@@ -30,3 +30,7 @@ jobs:
     uses: apple/swift-nio/.github/workflows/macos_tests.yml@main
     with:
       build_scheme: swift-distributed-tracing-Package
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main

.github/workflows/pull_request.yml

@@ -33,3 +33,7 @@ jobs:
   cxx-interop:
     name: Cxx interop
     uses: apple/swift-nio/.github/workflows/cxx_interop.yml@main
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main