bootstrap: Inhibit download-rustc in CI when tools are changed

[Zalathar]

This automatically avoids situations like #139998 (comment) and #140177 (comment), where a sensitive change to compiletest was eligible for download-rustc, preventing the collection of proper test metrics for comparison.

While the primary goal is to make compiletest changes inhibit download-rustc, this PR ends up making any change to src/tools inhibit download-rustc (but only in CI builds). With the current code, it's not clear how to “un-exempt” individual subdirectories that are covered by another exemption.

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See https://rust-lang.zulipchat.com/#narrow/channel/326414-t-infra.2Fbootstrap/topic/Should.20tool.20changes.20inhibit.20download-rustc.20on.20CI.3F for associated discussion.

[rustbot]

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[rustbot]

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

[jieyouxu]

r? @onur-ozkan (discussion in #t-infra/bootstrap > Should tool changes inhibit download-rustc on CI?)

[onur-ozkan]

Like I said on the Zulip thread, I think the proper solution would be to investigate and fix the issue of "some tests being ignored" rather than excluding tool paths from ci-rustc. Those tools don't have any effect on the rustc builds.

[onur-ozkan]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[bors]

☔ The latest upstream changes (presumably #119899) made this pull request unmergeable. Please resolve the merge conflicts.