Add alter_tables.cql to gitignore

The alter_tables.cql is being copied during build and should be ignored.

Change-Id: I0a0a420e17761247a6575ad8715ccbd20fd5c1e1
Issue-ID: SDC-2640
Signed-off-by: andre.schmid <andre.schmid@est.tech>
diff --git a/.gitignore b/.gitignore
index 51d111f..415b38f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -264,6 +264,7 @@
 
 /openecomp-be/dist/sdc-onboard-db-init-docker/artifacts/init_keyspaces.cql
 /openecomp-be/dist/sdc-onboard-db-init-docker/artifacts/init_schemas.cql
+/openecomp-be/dist/sdc-onboard-db-init-docker/artifacts/alter_tables.cql
 
 asdctool/*.csv
 asdctool/test-output/*