Support period lengthened for the 6.6, 6.12, and 6.18 kernels

The stated support periods for the 6.6, 6.12, and 6.18 kernels has been extended. The 6.6 kernel will be supported with stable updates through the end of 2027 (for four years of support total), while 6.12 and 6.18 will get updates through the end of 2028, for four and three years of support.