Enable release mode builds (#211)

### 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

@@ -26,3 +26,7 @@ jobs:
     name: Static SDK
     # Workaround https://github.com/nektos/act/issues/1875
     uses: apple/swift-nio/.github/workflows/static_sdk.yml@main
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main

.github/workflows/pull_request.yml

@@ -30,3 +30,7 @@ jobs:
     name: Static SDK
     # Workaround https://github.com/nektos/act/issues/1875
     uses: apple/swift-nio/.github/workflows/static_sdk.yml@main
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main