Fix missing vars in buildkite changesets.sh (#38830) (#38831)

PR #38814 missed a couple of patterns required
by the `defineModuleFromTheChangeSet()` function.

This commit adds the missing regex patters
needed for identifying module changesets.

(cherry picked from commit a3f7bae)

Co-authored-by: Dimitrios Liappis <dimitrios.liappis@gmail.com>

.buildkite/scripts/changesets.sh

@@ -2,6 +2,9 @@
 
 # This script contains helper functions related to what should be run depending on Git changes
 
+OSS_MODULE_PATTERN="^[a-z0-9]+beat\\/module\\/([^\\/]+)\\/.*"
+XPACK_MODULE_PATTERN="^x-pack\\/[a-z0-9]+beat\\/module\\/([^\\/]+)\\/.*"
+
 are_paths_changed() {
   local patterns=("${@}")
   local changelist=()