Amend wording of note

Author: davidhewitt

src/librustc_builtin_macros/format.rs

@@ -537,7 +537,7 @@ impl<'a, 'b> Context<'a, 'b> {
                                     name
                                 ));
                                 err.note(
-                                    "for hygiene reasons format_args! cannot capture variables \
+                                    "to avoid ambiguity format_args! cannot capture variables \
                                      when the format string is expanded from a macro",
                                 );
                             } else if self.ecx.parse_sess().unstable_features.is_nightly_build() {

src/test/ui/fmt/format-args-capture-macro-hygiene.stderr

@@ -5,7 +5,7 @@ LL |     format!(concat!("{foo}"));
    |             ^^^^^^^^^^^^^^^^
    |
    = note: did you intend to capture a variable `foo` from the surrounding scope?
-   = note: for hygiene reasons format_args! cannot capture variables when the format string is expanded from a macro
+   = note: to avoid ambiguity format_args! cannot capture variables when the format string is expanded from a macro
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: there is no argument named `bar`
@@ -15,7 +15,7 @@ LL |     format!(concat!("{ba", "r} {}"), 1);
    |             ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: did you intend to capture a variable `bar` from the surrounding scope?
-   = note: for hygiene reasons format_args! cannot capture variables when the format string is expanded from a macro
+   = note: to avoid ambiguity format_args! cannot capture variables when the format string is expanded from a macro
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors