Enable release mode builds (#850)

### 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

@@ -21,3 +21,7 @@ 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