composepost: Normalize rpmdb.sqlite-shm

In some testing I have using `SOURCE_DATE_EPOCH=0`, this file
is now the only thing that differs across builds.

rust/src/composepost.rs

@@ -274,6 +274,11 @@ fn postprocess_cleanup_rpmdb_impl(rootfs_dfd: &Dir) -> Result<()> {
         if matches!(name, ".dbenv.lock" | ".rpm.lock") || name.starts_with("__db.") {
             d.remove_file(name)?;
         }
+        // SQLite case.  Today, it seems to work to remove the WAL, but removing the SHM
+        // file causes a runtime error as RPM tries to mutate a read-only database.
+        if matches!(name, "rpmdb.sqlite-shm" | "rpmdb.sqlite-wal") {
+            d.write(name, b"")?;
+        }
     }
     Ok(())
 }