Fix some tests to *only* test their main issue and not have secondary failures

Author: oli-obk

tests/ui/type-alias-impl-trait/auto-trait-leakage3.rs

@@ -4,7 +4,7 @@
 // FIXME This should compile, but it currently doesn't
 
 mod m {
-    type Foo = impl std::fmt::Debug;
+    pub type Foo = impl std::fmt::Debug;
     //~^ ERROR: cycle detected when computing type of `m::Foo::{opaque#0}` [E0391]
 
     pub fn foo() -> Foo {

tests/ui/type-alias-impl-trait/auto-trait-leakage3.stderr

@@ -1,8 +1,8 @@
 error[E0391]: cycle detected when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/auto-trait-leakage3.rs:7:16
+  --> $DIR/auto-trait-leakage3.rs:7:20
    |
-LL |     type Foo = impl std::fmt::Debug;
-   |                ^^^^^^^^^^^^^^^^^^^^
+LL |     pub type Foo = impl std::fmt::Debug;
+   |                    ^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires type-checking `m::bar`...
   --> $DIR/auto-trait-leakage3.rs:15:9

tests/ui/type-alias-impl-trait/inference-cycle.rs

@@ -2,7 +2,7 @@
 #![allow(dead_code)]
 
 mod m {
-    type Foo = impl std::fmt::Debug;
+    pub type Foo = impl std::fmt::Debug;
     //~^ ERROR cycle detected
 
     // Cycle: error today, but it'd be nice if it eventually worked
@@ -16,7 +16,7 @@ mod m {
     }
 
     fn baz() {
-        let f: Foo = 22_u32;
+        let f: Foo = ();
     }
 
     fn is_send<T: Send>(_: T) {}

tests/ui/type-alias-impl-trait/inference-cycle.stderr

@@ -1,8 +1,8 @@
 error[E0391]: cycle detected when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/inference-cycle.rs:5:16
+  --> $DIR/inference-cycle.rs:5:20
    |
-LL |     type Foo = impl std::fmt::Debug;
-   |                ^^^^^^^^^^^^^^^^^^^^
+LL |     pub type Foo = impl std::fmt::Debug;
+   |                    ^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires type-checking `m::bar`...
   --> $DIR/inference-cycle.rs:15:9