fix: change fgac database role tags

[asthamohta]

No description provided.

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• samples/samples/snippets.py:2317, tag spanner_add_and_drop_database_role

You are about to delete 1 region tag.

• samples/samples/snippets.py:2317, tag spanner_add_and_drop_database_roles

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