fix: join paths when passing args to forge build (#8371)

* fix: join paths when passing args to forge build

* fmt

---------

Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

Author: klkvr

crates/forge/bin/cmd/build.rs

@@ -93,6 +93,8 @@ impl BuildArgs {
         let mut files = vec![];
         if let Some(paths) = &self.paths {
             for path in paths {
+                let joined = project.root().join(path);
+                let path = if joined.exists() { &joined } else { path };
                 files.extend(source_files_iter(path, MultiCompilerLanguage::FILE_EXTENSIONS));
             }
         }