Improve warning message grammar

Author: Nemo157

src/cargo/core/workspace.rs

@@ -1006,7 +1006,7 @@ impl<'cfg> Workspace<'cfg> {
                         self.config.shell().warn(
                             format_args!("\
                         some crates are on edition {edition} which defaults to `resolver = \"{resolver}\"`,\n\
-                     \x20   but a virtual workspace defaults to `resolver = \"1\"`\n\
+                     \x20   but virtual workspaces default to `resolver = \"1\"`\n\
                      \x20   specify the desired resolver version explicitly in the workspace root's manifest\
                             ",
                         ))?;

tests/testsuite/features2.rs

@@ -1432,7 +1432,7 @@ fn edition_2021_workspace_member() {
         .with_stderr(
             "\
 warning: some crates are on edition 2021 which defaults to `resolver = \"2\"`,
-    but a virtual workspace defaults to `resolver = \"1\"`
+    but virtual workspaces default to `resolver = \"1\"`
     specify the desired resolver version explicitly in the workspace root's manifest
 [CHECKING] a v0.1.0 [..]
 [FINISHED] [..]