githooks: fix push reject when hbl is directly based on hbk

The issue this fixes is that git reports same commit as being ancestor
of itself. It kind of makes sense but it breaks check if branch is based
on hbk or hbl or hbd. In such case for example the common base between
hbl and target branch and hbk and target branch is the same.

This changes the logic. Because git merge-base does effectively the
operation of 'less than or equal' we have to swap compare order and
negate the result. This way we get effectively the 'less than'
operation.
8 jobs for hotfix/githook-same-base in 6 minutes and 18 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Build
passed #515323
lists_generate

00:00:32

passed #515320
medkit_mox

00:06:18

passed #515321
medkit_omnia

00:05:37

passed #515322
medkit_turris1x

00:03:12

passed #515317
prepare_mox

00:02:46

passed #515318
prepare_omnia

00:02:45

passed #515319
prepare_turris1x

00:02:45

 
  Verify
passed #515324
lists_verify

00:00:26