checker: allow for _ being used as both import x as _ and fn f(_ int) { (fix (#26219) #26230

Author: felipensp

vlib/v/checker/checker.v

@@ -6073,6 +6073,9 @@ fn (mut c Checker) deprecate_old_isreftype_and_sizeof_of_a_guessed_type(is_guess
 }
 
 fn (c &Checker) check_import_sym_conflict(ident string) bool {
+	if ident == '_' {
+		return false
+	}
 	for import_sym in c.file.imports {
 		// Check if alias exists or not
 		if !import_sym.alias.is_blank() {

vlib/v/checker/tests/discard_import_usage.out

@@ -0,0 +1,7 @@
+import os as _
+
+fn test_fn(_ int) {}
+
+fn main() {
+	test_fn(12)
+}