fix: update rpm release tag to el8 (microsoft#203770)

Author: deepak1556

resources/linux/rpm/code.spec.template

@@ -1,6 +1,6 @@
 Name:     @@NAME@@
 Version:  @@VERSION@@
-Release:  @@RELEASE@@.el7
+Release:  @@RELEASE@@.el8
 Summary:  Code editing. Redefined.
 Group:    Development/Tools
 Vendor:   Microsoft Corporation