build runners are cached causing overrides to be ignored

[xdBronch]

Zig Version

0.12.0-dev.2015+60958d135

Steps to Reproduce and Observed Behavior

run zig build on any project
run zig build --build-runner failing_runner.zig

// failing_runner.zig
pub fn main() void {
    @import("std").process.exit(1);
}

build still succeeds

delete local cache and rerun with failing runner
build fails

run without --build-runner
build still fails

Expected Behavior

build runner should be respected with each invocation of the build system, regression from #18160