Spec.__str__: use full hash (spack#47322)

The idea is that `spack -e env add ./concrete-spec.json` would list the
full hash in the specs, so that (a) it's not ambiguous and (b) it could
in principle results in constant time lookup instead of linear time
substring match in large build caches.

lib/spack/spack/spec.py

@@ -4042,7 +4042,7 @@ def format_path(
 
     def __str__(self):
         if self._concrete:
-            return self.format("{name}{@version}{/hash:7}")
+            return self.format("{name}{@version}{/hash}")
 
         if not self._dependencies:
             return self.format()