fix(core-flows): export updateTaxRegionsStep (#10732)

Export `updateTaxRegionsStep` to ensure it's included in generated references

.changeset/chatty-zebras-smash.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/core-flows": patch
+---
+
+fix(core-flows): export updateTaxRegionsStep

packages/core/core-flows/src/tax/steps/index.ts

@@ -8,3 +8,4 @@ export * from "./delete-tax-rate-rules"
 export * from "./create-tax-rate-rules"
 export * from "./list-tax-rate-rule-ids"
 export * from "./list-tax-rate-ids"
+export * from "./update-tax-regions"