radicle-fetch: Fallback to known version

There's a good chance that gix can just keep going in this case.

crates/radicle-fetch/src/transport.rs

@@ -327,9 +327,15 @@ impl WantsHaves {
     }
 }
 
-fn agent_name() -> io::Result<String> {
-    Ok(format!(
-        "git/{}",
-        radicle::git::version().map_err(io_other)?
-    ))
+fn agent_name() -> String {
+    let version = match radicle::git::version() {
+        Ok(version) => version,
+        Err(err) => {
+            use radicle::git::VERSION_REQUIRED;
+            log::warn!(target: "fetch", "The git version could not be determined: {err}");
+            log::warn!(target: "fetch", "Pretending that we are on git version {VERSION_REQUIRED}.");
+            VERSION_REQUIRED
+        }
+    };
+    format!("git/{version}")
 }

crates/radicle-fetch/src/transport/fetch.rs

@@ -174,7 +174,7 @@ where
         keepfile: None,
     };
     let mut negotiate = Negotiate { wants_haves };
-    let agent = agent_name().map_err(Error::ReadRemainingBytes)?;
+    let agent = agent_name();
 
     let mut pack_out = None;
     let mut handshake = handshake.clone();

crates/radicle-fetch/src/transport/ls_refs.rs

@@ -60,7 +60,7 @@ where
                 arg.push_str(prefix);
                 args.push(arg)
             }
-            features.push(("agent", Some(Cow::Owned(agent_name()?))));
+            features.push(("agent", Some(Cow::Owned(agent_name()))));
             Ok(gix_protocol::ls_refs::Action::Continue)
         },
         progress,