Bump gradle-plugins in /conventions

Bumps gradle-plugins from 1.9.1-alpha to 1.19.0-alpha-SNAPSHOT.

---
updated-dependencies:
- dependency-name: io.opentelemetry.instrumentation:gradle-plugins
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

conventions/build.gradle.kts

@@ -33,7 +33,7 @@ dependencies {
   implementation(gradleApi())
   implementation(localGroovy())
 
-  implementation("io.opentelemetry.instrumentation:gradle-plugins:1.9.1-alpha")
+  implementation("io.opentelemetry.instrumentation:gradle-plugins:1.19.0-alpha-SNAPSHOT")
 
   implementation("org.eclipse.aether:aether-connector-basic:1.1.0")
   implementation("org.eclipse.aether:aether-transport-http:1.1.0")