cli: include message from GitExportError to user

I'm going to add other error variants for when we fail to read/write
to disk, and I don't think we need to have a custom message for each
in the CLI crate. It's easier to pass along the message from the lib
crate.

(`ConflictedBranch`, on the other hand, is an expected error so I
think we should continue to let let the CLI crate define the error
message for it.)

lib/src/git.rs

@@ -166,7 +166,7 @@ pub fn import_refs(
 pub enum GitExportError {
     #[error("Cannot export conflicted branch '{0}'")]
     ConflictedBranch(String),
-    #[error("Unexpected git error when exporting refs: {0}")]
+    #[error("Git error: {0}")]
     InternalGitError(#[from] git2::Error),
 }
 

src/cli_util.rs

@@ -169,7 +169,7 @@ impl From<GitExportError> for CommandError {
             GitExportError::ConflictedBranch(branch_name) => {
                 user_error(format!("Cannot export conflicted branch '{branch_name}'"))
             }
-            GitExportError::InternalGitError(err) => CommandError::InternalError(format!(
+            err => CommandError::InternalError(format!(
                 "Failed to export refs to underlying Git repo: {err}"
             )),
         }