Update error message to not start with capital letters

Signed-off-by: hi-rustin <rustin.liu@gmail.com>

Author: 0xPoe

src/cargo/util/toml_mut/dependency.rs

@@ -279,7 +279,7 @@ impl Dependency {
                     let src = WorkspaceSource::new();
                     src.into()
                 } else {
-                    let mut msg = format!("Unrecognized dependency source for `{key}`");
+                    let mut msg = format!("unrecognized dependency source for `{key}`");
                     if table.is_empty() {
                         msg.push_str(
                         ", expected a table with a `version`, `git`, `path`, or `workspace` key",

tests/testsuite/cargo_add/empty_dep_table/stderr.log

@@ -1 +1 @@
-error: Unrecognized dependency source for `your-face`, expected a table with a `version`, `git`, `path`, or `workspace` key
+error: unrecognized dependency source for `your-face`, expected a table with a `version`, `git`, `path`, or `workspace` key