ci: bump timeout for tests to 15 minutes

We've been seing longer runs on release CI for nightlies, possibly due
to more than 2 parallel builds running on one host.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

ci/Jenkinsfile.tests

@@ -9,7 +9,7 @@ pipeline {
   options {
     timestamps()
     /* Prevent Jenkins jobs from running forever */
-    timeout(time: 10, unit: 'MINUTES')
+    timeout(time: 15, unit: 'MINUTES')
     /* Limit builds retained */
     buildDiscarder(logRotator(
       numToKeepStr: '10',