ISSDK-1893: CI: Fix Gradle setup on Linux/Windows and update GitHub Actions off deprecated Node.js 20

[sagadira]

Summary

Fixes CI infrastructure issues in the GitHub Actions workflows for CiscoM31/openapi-generator. These changes were previously bundled in PR #176 (ISSDK-692) and have been split out into their own PR under ISSDK-1893.

Changes

.github/workflows/linux.yaml

• Add gradle/actions/setup-gradle@v6 with pinned gradle-version: 8.14.3
• Add cache: gradle to setup-java steps
• Update Gradle command syntax from gradle -b <build.gradle> to gradle --project-dir <dir>
• Update upload-artifact to v7

.github/workflows/windows.yaml

• Add gradle-version parameter to the Windows Gradle setup
• Add cache: gradle to setup-java steps

GitHub Actions Node.js 20 deprecation

• Update actions to v5 (checkout@v5, setup-java@v5, cache@v5, download-artifact@v5), upload-artifact@v7, and s4u/setup-maven-action@v1.20.0 to move off the deprecated Node.js 20 runner.

Why

• The Linux/Windows Gradle jobs were failing due to an unmanaged/incompatible Gradle version. Pinning Gradle 8.14.3 via gradle/actions/setup-gradle@v6 and using --project-dir makes the builds reproducible.
• GitHub deprecated the Node.js 20 action runtime; older action versions emit deprecation warnings and will eventually fail. Bumping to v5/v7 actions resolves this.

Related

• Split out from PR ISSDK-692: Support text/plain JSON responses in Go SDK decode() #176 (ISSDK-692: text/plain JSON responses in Go SDK decode()), which now contains only the Go SDK fix.
• JIRA: ISSDK-1893