Enable release mode builds (#40)

### 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

@@ -34,3 +34,7 @@ jobs:
       build_scheme: swift-nio-oblivious-http-Package
       xcode_16_2_build_arguments_override: "-Xswiftc -Xfrontend -Xswiftc -require-explicit-sendable"
       xcode_16_3_build_arguments_override: "-Xswiftc -Xfrontend -Xswiftc -require-explicit-sendable"
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main

.github/workflows/pull_request.yml

@@ -38,3 +38,7 @@ jobs:
       build_scheme: swift-nio-oblivious-http-Package
       xcode_16_2_build_arguments_override: "-Xswiftc -Xfrontend -Xswiftc -require-explicit-sendable"
       xcode_16_3_build_arguments_override: "-Xswiftc -Xfrontend -Xswiftc -require-explicit-sendable"
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main