fix(renovate): enable updates for opentelemetry-instrumentation-bom-alpha (#1860)

The opentelemetry-instrumentation-bom-alpha dependency was not being
updated by Renovate despite newer versions being available (currently on
2.16.0-alpha, but 2.24.0-alpha is available).

Root cause: Renovate was detecting the dependency but not creating PRs
due to the default ignoreUnstable behavior in the recommended preset.
Since this package only publishes alpha versions, we need to explicitly
allow unstable version updates.

Solution: Added a packageRule with ignoreUnstable: false for this
specific package to ensure Renovate will create PRs for newer alpha
versions.

---------

Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

.github/renovate.json5

@@ -23,6 +23,10 @@
       groupName: "java graalvm",
       additionalBranchPrefix: "graalvm-",
     },
+    {
+      matchPackageNames: ["io.opentelemetry.instrumentation:opentelemetry-instrumentation-bom-alpha"],
+      ignoreUnstable: false,
+    },
   ],
   customManagers: [
     {