roll: recipes_version.txt variable_roll: Move regex to separate method

This simplifies the diff for an upcoming change.

Original-Bug: b/422157791
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/297052
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: d1f7f16f3012447dc3b82835176d58e729427014
GitOrigin-RevId: 0786cdb0d54f63cb136e9c9ca0c8de299a9decb7
Change-Id: I5572065d27a775ba0440467b6fcdbcdbd2687056
diff --git a/recipes_version.txt b/recipes_version.txt
index aada841..4aca49a 100644
--- a/recipes_version.txt
+++ b/recipes_version.txt
@@ -1 +1 @@
-c98c5756963a915c0e60b90edfc3c555c81ce6e8
+d1f7f16f3012447dc3b82835176d58e729427014