Change wording to less jaron-y "non-auto trait"

Co-authored-by: Vadim Petrochenkov <[email protected]>

Author: notriddle

compiler/rustc_typeck/src/coherence/inherent_impls.rs

@@ -67,7 +67,7 @@ impl ItemLikeVisitor<'v> for InherentCollect<'tcx> {
                     E0785,
                     "cannot define inherent `impl` for a dyn auto trait"
                 )
-                .span_label(ty.span, "impl requires a principal trait")
+                .span_label(ty.span, "impl requires at least one non-auto trait")
                 .note("define and implement a new trait or type instead")
                 .emit();
             }

src/test/ui/coherence/issue-85026.stderr

@@ -2,15 +2,15 @@ error[E0785]: cannot define inherent `impl` for a dyn auto trait
   --> $DIR/issue-85026.rs:5:6
    |
 LL | impl dyn AutoTrait {}
-   |      ^^^^^^^^^^^^^ impl requires a principal trait
+   |      ^^^^^^^^^^^^^ impl requires at least one non-auto trait
    |
    = note: define and implement a new trait or type instead
 
 error[E0785]: cannot define inherent `impl` for a dyn auto trait
   --> $DIR/issue-85026.rs:8:6
    |
 LL | impl dyn Unpin {}
-   |      ^^^^^^^^^ impl requires a principal trait
+   |      ^^^^^^^^^ impl requires at least one non-auto trait
    |
    = note: define and implement a new trait or type instead