Walk back to the root context to compute the span (#14349)

Since the error kind (`io::ErrorKind::other`) is in the root context,
the error message must be found in the root context as well to compute
the correct span to remove.

Fix #14346

changelog: [`io_error_other`]: fix non-applicable suggestion

r? @llogiq

tests/ui/io_other_error.fixed

@@ -53,3 +53,8 @@ mod paths {
 fn under_msrv() {
     let _err = std::io::Error::new(std::io::ErrorKind::Other, E);
 }
+
+pub fn issue14346(x: i32) -> std::io::Error {
+    std::io::Error::other(format!("{x}"))
+    //~^ ERROR: this can be `std::io::Error::other(_)`
+}

tests/ui/io_other_error.rs

@@ -53,3 +53,8 @@ mod paths {
 fn under_msrv() {
     let _err = std::io::Error::new(std::io::ErrorKind::Other, E);
 }
+
+pub fn issue14346(x: i32) -> std::io::Error {
+    std::io::Error::new(std::io::ErrorKind::Other, format!("{x}"))
+    //~^ ERROR: this can be `std::io::Error::other(_)`
+}

tests/ui/io_other_error.stderr

@@ -48,5 +48,17 @@ LL -         let _err = io::Error::new(io::ErrorKind::Other, super::E);
 LL +         let _err = io::Error::other(super::E);
    |
 
-error: aborting due to 4 previous errors
+error: this can be `std::io::Error::other(_)`
+  --> tests/ui/io_other_error.rs:58:5
+   |
+LL |     std::io::Error::new(std::io::ErrorKind::Other, format!("{x}"))
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: use `std::io::Error::other`
+   |
+LL -     std::io::Error::new(std::io::ErrorKind::Other, format!("{x}"))
+LL +     std::io::Error::other(format!("{x}"))
+   |
+
+error: aborting due to 5 previous errors