Fix OSGi test setup: version syntax typo and testingBundle classpath

[zeitlinger]

Two small fixes found during review of open-telemetry#7964 (open-telemetry/opentelemetry-java).

Fix 1: Missing = in version constraint string

In otel.java-conventions.gradle.kts, the Kotlin string produced version"${@}" instead of version="${@}" — a one-character typo. The test bundle in this same PR had it right; the conventions file didn't.

BND's lenient parser accepts both forms so the generated manifest is correct either way, but the code is wrong and inconsistent.

Fix 2: testingBundle classpath causes silent test no-ops

The Bundle task uses compileClasspath by default for BND analysis. This means testImplementation dependencies are invisible to BND — including the @Testable annotation needed by the Test-Cases macro. With JUnit in testImplementation, BND can't resolve @Testable, the Test-Cases header comes out empty, 0 tests are discovered, and the task reports success regardless of whether any assertions would have failed.

Fix: add classpath(sourceSets.test.get().runtimeClasspath) to testingBundleTask, which makes testImplementation deps visible to BND and allows junit-jupiter to move back to testImplementation where it belongs.