[2027] Add systemcore as a photonlib build target (#1995)

## Description

Added systemcore to a couple of build files in order for `./gradlew
publishToMavenLocal` to generate systemcore-compatible dependencies.

Needed to support deploying photonlib to systemcore.

## Meta

Merge checklist:
- [x] Pull Request title is [short, imperative
summary](https://cbea.ms/git-commit/) of proposed changes
- [x] The description documents the _what_ and _why_
- [ ] If this PR changes behavior or adds a feature, user documentation
is updated
- [ ] If this PR touches photon-serde, all messages have been
regenerated and hashes have not changed unexpectedly
- [ ] If this PR touches configuration, this is backwards compatible
with settings back to v2024.3.1
- [ ] If this PR touches pipeline settings or anything related to data
exchange, the frontend typing is updated
- [ ] If this PR addresses a bug, a regression test for it is added

---------

Co-authored-by: Gold856 <117957790+Gold856@users.noreply.github.com>

.github/workflows/build.yml

@@ -266,6 +266,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - container: wpilib/systemcore-cross-ubuntu:2025-24.04
+            artifact-name: SystemCore
+            build-options: "-Ponlylinuxsystemcore"
           - container: wpilib/raspbian-cross-ubuntu:bookworm-24.04
             artifact-name: Raspbian
             build-options: "-Ponlylinuxarm32"