Only show images during tests when requested via project property (#2177)

## Description

Revision of #2164. Instead of only running headless tests during a
build, now only the images are disabled. To reenable showing images, the
`enableTestUi` project property needs to be passed to gradle.

```bash
./gradlew test -PenableTestUi
```

## 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_
- [X] This PR has been
[linted](https://docs.photonvision.org/en/latest/docs/contributing/linting.html).
- [x] 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 v2025.3.2
- [ ] 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

.github/workflows/build.yml

@@ -88,10 +88,8 @@ jobs:
         run: sudo apt-get update && sudo apt-get install -y libcholmod3 liblapack3 libsuitesparseconfig5
       - name: Gradle Build
         run: ./gradlew photon-targeting:build photon-core:build photon-server:build -x check
-      - name: Gradle Tests
-        run: ./gradlew testHeadless --stacktrace
-      - name: Gradle Coverage
-        run: ./gradlew jacocoTestReport
+      - name: Gradle Tests and Coverage
+        run: ./gradlew test jacocoTestReport --stacktrace
   build-offline-docs:
     name: "Build Offline Docs"
     runs-on: ubuntu-22.04