Extend maven-checks job timeout by additional 5 minutes

The recent merge of trinodb#16098
increased build robustness in the event of main Ubuntu repo failures,
at the cost of 2-3 minutes for downloading Ubuntu mirror indexes.

It turns out the 45 minute timeout was very close to the actual time
needed to perform the entire job, and extending it is
necessary to avoid cancelling the job.

.github/workflows/ci.yml

@@ -58,7 +58,7 @@ jobs:
         java-version:
           - 17
           - 20
-    timeout-minutes: 45
+    timeout-minutes: 50
     steps:
       - uses: actions/checkout@v3
         with: