Auto merge of #135173 - pietroalbini:pa-fix-rvp, r=workingjubilee

Avoid replacing the definition of `CURRENT_RUSTC_VERSION`

Before this PR, replace-version-placeholder hardcoded the path defining CURRENT_RUSTC_VERSION (to avoid replacing it). After a refactor moved the file defining it without changing the hardcoded path, the tool started replacing the constant itself with the version number.

To avoid this from happening in the future, this changes the definition of the constant to avoid the tool from ever matching it.

r? `@workingjubilee`