Rename test modules for previously included files.

(cherry picked from commit 75e2bde5fb)

jaarg/src/option.rs

@@ -241,7 +241,7 @@ impl core::ops::BitOr for OptFlag {
 }
 
 #[cfg(test)]
-mod opt_tests {
+mod tests {
   use super::*;
 
   #[test]

jaarg/src/options.rs

@@ -79,7 +79,7 @@ impl<ID: 'static> Opts<ID> {
 
 
 #[cfg(test)]
-mod opts_tests {
+mod tests {
   use super::*;
 
   #[test]