Add beta- and nightly-specific expected stderr

It looks like some commit started reporting conflicting trait impls
using an un-qualified trait name, rather than a fully qualified one.
This is a minor cosmetic detail, as far as these tests are concerned. We
should be able to unify these again when 1.67 hits stable in a few
weeks.

num_enum/tests/try_build/compile_fail/conflicting_default.stderr_beta

@@ -0,0 +1,9 @@
+error[E0119]: conflicting implementations of trait `Default` for type `Number`
+ --> tests/try_build/compile_fail/conflicting_default.rs:1:19
+  |
+1 | #[derive(Default, num_enum::Default)]
+  |          -------  ^^^^^^^^^^^^^^^^^ conflicting implementation for `Number`
+  |          |
+  |          first implementation here
+  |
+  = note: this error originates in the derive macro `num_enum::Default` (in Nightly builds, run with -Z macro-backtrace for more info)

num_enum/tests/try_build/compile_fail/conflicting_default.stderr_nightly

@@ -0,0 +1,9 @@
+error[E0119]: conflicting implementations of trait `Default` for type `Number`
+ --> tests/try_build/compile_fail/conflicting_default.rs:1:19
+  |
+1 | #[derive(Default, num_enum::Default)]
+  |          -------  ^^^^^^^^^^^^^^^^^ conflicting implementation for `Number`
+  |          |
+  |          first implementation here
+  |
+  = note: this error originates in the derive macro `num_enum::Default` (in Nightly builds, run with -Z macro-backtrace for more info)

num_enum/tests/try_build/compile_fail/conflicting_derive.stderr_beta

@@ -0,0 +1,20 @@
+error[E0119]: conflicting implementations of trait `TryFromPrimitive` for type `Numbers`
+ --> tests/try_build/compile_fail/conflicting_derive.rs:1:35
+  |
+1 | #[derive(num_enum::FromPrimitive, num_enum::TryFromPrimitive)]
+  |          -----------------------  ^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Numbers`
+  |          |
+  |          first implementation here
+  |
+  = note: this error originates in the derive macro `num_enum::TryFromPrimitive` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `TryFrom<u8>` for type `Numbers`
+ --> tests/try_build/compile_fail/conflicting_derive.rs:1:35
+  |
+1 | #[derive(num_enum::FromPrimitive, num_enum::TryFromPrimitive)]
+  |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: conflicting implementation in crate `core`:
+          - impl<T, U> TryFrom<U> for T
+            where U: Into<T>;
+  = note: this error originates in the derive macro `num_enum::TryFromPrimitive` (in Nightly builds, run with -Z macro-backtrace for more info)

num_enum/tests/try_build/compile_fail/conflicting_derive.stderr_nightly

@@ -0,0 +1,20 @@
+error[E0119]: conflicting implementations of trait `TryFromPrimitive` for type `Numbers`
+ --> tests/try_build/compile_fail/conflicting_derive.rs:1:35
+  |
+1 | #[derive(num_enum::FromPrimitive, num_enum::TryFromPrimitive)]
+  |          -----------------------  ^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Numbers`
+  |          |
+  |          first implementation here
+  |
+  = note: this error originates in the derive macro `num_enum::TryFromPrimitive` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `TryFrom<u8>` for type `Numbers`
+ --> tests/try_build/compile_fail/conflicting_derive.rs:1:35
+  |
+1 | #[derive(num_enum::FromPrimitive, num_enum::TryFromPrimitive)]
+  |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: conflicting implementation in crate `core`:
+          - impl<T, U> TryFrom<U> for T
+            where U: Into<T>;
+  = note: this error originates in the derive macro `num_enum::TryFromPrimitive` (in Nightly builds, run with -Z macro-backtrace for more info)