Turn off the KUnit fault test in the test fragments

[tamnd]

On 6.12.111 the boot unit failed for both the gcc kernel and the rucc kernel in every KUnit run. The cause is the kunit_fault suite. 6.12 builds it by default (CONFIG_KUNIT_FAULT_TEST=y), and it dereferences NULL on purpose to show that KUnit survives a fault. The test fragment sets CONFIG_PANIC_ON_OOPS=y and the command line has oops=panic, so that oops ends the run. Every suite after kunit_fault did not run, and the 6.12 grade counted only 123 units.

This change turns CONFIG_KUNIT_FAULT_TEST off in the fragments for E8 to E11. A missing symbol asked to be n counts as taken, so kernels without the symbol (6.1) and kernels that already default it to off (7.2) do not change. The setting is the same for both builds, so the grade stays fair.

Changes:

• configs/test.fragment.E*: add # CONFIG_KUNIT_FAULT_TEST is not set after CONFIG_KUNIT_ALL_TESTS=m, and say in the header that this is the one thing the fragment turns off.
• docs/plan/11-boot-and-tests.md: show the line in 11.1 and add a note that gives the reason.
• crates/rk/src/kconfig.rs: the_committed_fragments_read now checks that each fragment turns the fault test off.

Tested on server2: cargo fmt --check -p rk and cargo test -p rk kconfig (8 passed). The 6.12.111 X64 and X32 grades are being run again with the new fragment.