`term.svg` files get the wrong `width` calculated when using variable substitution

```diff
---- expected: tests/testsuite/cargo_remove/invalid_package/stderr.term.svg
++++ actual:   stderr
   1      - <svg width="890.4000000000001px" height="36px" xmlns="http://www.w3.org/2000/svg">
        1 + <svg width="882px" height="36px" xmlns="http://www.w3.org/2000/svg">

````
See https://github.com/rust-lang/cargo/pull/13461#discussion_r1495028555