Ignore cargo mutants output

Author: katediadechko

Rust.gitignore

@@ -13,9 +13,13 @@ Cargo.lock
 # MSVC Windows builds of rustc generate these, which store debugging information
 *.pdb
 
+# Generated by cargo mutants
+# Contains mutation testing data
+**/mutants.out*/
+
 # RustRover
 #  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
 #  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
 #  and can be added to the global gitignore or merged into this file.  For a more nuclear
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
-#.idea/
+#.idea/