sql: make all queries persistent and update to upstream sqlx

&str queries are not persistent by default.  To make queries persistent,
they have to be constructed with sqlx::query.

Upstream sqlx does not contain the change that make all queries
persistent, but it is not needed anymore. but

src/config.rs

@@ -242,7 +242,7 @@ impl Context {
         match key {
             Config::Selfavatar => {
                 self.sql
-                    .execute("UPDATE contacts SET selfavatar_sent=0;")
+                    .execute(sqlx::query("UPDATE contacts SET selfavatar_sent=0;"))
                     .await?;
                 self.sql
                     .set_raw_config_bool("attach_selfavatar", true)