Use upgraded CI images
See !683 (merged). Removes workarounds for fixed false positives in IWYU 0.16, moves thread sanitizer job to the optional section (see #440), and pins a new CI image.
See !683 (merged). Removes workarounds for fixed false positives in IWYU 0.16, moves thread sanitizer job to the optional section (see #440), and pins a new CI image.