Use consistent prose for ::

Co-authored-by: Camille Gillot <gillot.camille@gmail.com>

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -2080,7 +2080,7 @@ impl<'a> Parser<'a> {
                     // Find a mistake like "foo::var:A".
                     err.span_suggestion(
                         snapshot.token.span,
-                        "you might have meant to write a path",
+                        "write a path separator here",
                         "::".to_string(),
                         Applicability::MaybeIncorrect,
                     );

src/test/ui/generics/single-colon-path-not-const-generics.rs

@@ -7,7 +7,7 @@ pub mod foo {
 pub struct Foo {
   a: Vec<foo::bar:A>,
   //~^ ERROR expected
-  //~| HELP you might have meant to write a path
+  //~| HELP path separator
 }
 
 fn main() {}

src/test/ui/generics/single-colon-path-not-const-generics.stderr

@@ -5,7 +5,7 @@ LL |   a: Vec<foo::bar:A>,
    |                  ^
    |                  |
    |                  expected one of `,` or `>`
-   |                  help: you might have meant to write a path: `::`
+   |                  help: write a path separator here: `::`
 
 error: aborting due to previous error