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

@@ -16,3 +16,7 @@ jobs:
       linux_6_1_arguments_override: "--explicit-target-dependency-import-check error"
       linux_nightly_next_arguments_override: "--explicit-target-dependency-import-check error"
       linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error"
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main

.github/workflows/pull_request.yml

@@ -45,3 +45,7 @@ jobs:
     with:
       name: "Cxx interop"
       matrix_string: '${{ needs.construct-cxx-matrix.outputs.cxx-interop-matrix }}'
+
+  release-builds:
+    name: Release builds
+    uses: apple/swift-nio/.github/workflows/release_builds.yml@main