BOM release document: replace_string to use variables (#1988)

* Updating release document

* Added a new variant found in cl/368721221

Co-authored-by: Elliotte Rusty Harold <elharo@users.noreply.github.com>

Author: suztomo

boms/cloud-oss-bom/RELEASING.md

@@ -96,8 +96,11 @@ new release is available on Maven Central.
 * Manually edit and update any pom.xml files in https://github.com/GoogleCloudPlatform/java-docs-samples that dependabot missed
 * In google3 run:
     * `$ g4d -f bom`
-    * `/google/src/head/depot/google3/devtools/scripts/replace_string "<version>oldVersion</version>" "<version>newVersion</version>"`
-    * `/google/src/head/depot/google3/devtools/scripts/replace_string "<version>oldVersion</version>" "<version>newVersion</version>"`
+    * `$ OLD=19.0.0; NEW=19.1.0`
+      (Adjust the old and new versions)
+    * `/google/src/head/depot/google3/devtools/scripts/replace_string "<version>${OLD}</version>" "<version>${NEW}</version>"`
+    * `/google/src/head/depot/google3/devtools/scripts/replace_string "<version>${OLD}</version>" "<version>${NEW}</version>"`
+    * `/google/src/head/depot/google3/devtools/scripts/replace_string "<version>${OLD}</version>" "<version>${NEW}</version>"`
     * Sanity check the cl and send it for review.
     * Submit on approval
 * Search for libraries-bom in google3 to find any internal references (typically cloudsite and devsite) that still need to be updated.