Move `tests/ui/{unreachable-code => reachable}`

... since unreachable-code only has a few tests while
`reachable` is the more popular directory...

tests/ui/reachable/boolean-negation-in-unreachable-code-7344.rs

diff --git a/tests/ui/unreachable-code/boolean-negation-in-unreachable-code-7344.rs b/tests/ui/reachable/boolean-negation-in-unreachable-code-7344.rs
similarity index 100%
rename from tests/ui/unreachable-code/boolean-negation-in-unreachable-code-7344.rs
rename to tests/ui/reachable/boolean-negation-in-unreachable-code-7344.rs

tests/ui/reachable/nested_type_ascription.rs

diff --git a/tests/ui/unreachable-code/nested_type_ascription.rs b/tests/ui/reachable/nested_type_ascription.rs
similarity index 99%
rename from tests/ui/unreachable-code/nested_type_ascription.rs
rename to tests/ui/reachable/nested_type_ascription.rs
index 9423082..1712ee0 100644
--- a/tests/ui/unreachable-code/nested_type_ascription.rs
+++ b/tests/ui/reachable/nested_type_ascription.rs
@@ -17,4 +17,3 @@ fn main() {
         ();
     }
 }
-

tests/ui/reachable/unreachable-bool-read-7246.rs

diff --git a/tests/ui/unreachable-code/unreachable-bool-read-7246.rs b/tests/ui/reachable/unreachable-bool-read-7246.rs
similarity index 100%
rename from tests/ui/unreachable-code/unreachable-bool-read-7246.rs
rename to tests/ui/reachable/unreachable-bool-read-7246.rs

tests/ui/reachable/unreachable-bool-read-7246.stderr

diff --git a/tests/ui/unreachable-code/unreachable-bool-read-7246.stderr b/tests/ui/reachable/unreachable-bool-read-7246.stderr
similarity index 100%
rename from tests/ui/unreachable-code/unreachable-bool-read-7246.stderr
rename to tests/ui/reachable/unreachable-bool-read-7246.stderr