Fix listen_addr help default value (#4812)

# Description of Changes

Fix the `spacetime start --listen-addr` help text to match the actual
default value.

The flag already defaults to `0.0.0.0:3000`, but the help text
incorrectly said port 80.

# API and ABI breaking changes
None.

# Expected complexity level and risk
Complexity 1.

# Testing
- [x] `cargo fmt --all --check`
- [x] `cargo check -p spacetimedb-standalone`

Co-authored-by: clockwork-labs-bot <clockwork-labs-bot@users.noreply.github.com>
Co-authored-by: Tyler Cloutier <cloutiertyler@users.noreply.github.com>

crates/standalone/src/subcommands/start.rs

@@ -34,7 +34,7 @@ pub fn cli() -> clap::Command {
                 .default_value("0.0.0.0:3000")
                 .help(
                     "The address and port where SpacetimeDB should listen for connections. \
-                     This defaults to to listen on all IP addresses on port 80.",
+                     This defaults to listening on all IP addresses on port 3000.",
                 ),
         )
         .arg(