Fix verifyCommits error when push a new branch (#26664)

> ### Description
> If a new branch is pushed, and the repository has a rule that would
require signed commits for the new branch, the commit is rejected with a
500 error regardless of whether it's signed.
> 
> When pushing a new branch, the "old" commit is the empty ID
(0000000000000000000000000000000000000000). verifyCommits has no
provision for this and passes an invalid commit range to git rev-list.
Prior to 1.19 this wasn't an issue because only pre-existing individual
branches could be protected.
> 
> I was able to reproduce with
[try.gitea.io/CraigTest/test](https://try.gitea.io/CraigTest/test),
which is set up with a blanket rule to require commits on all branches.


Fix #25565
Very thanks to @Craig-Holmquist-NTI for reporting the bug and suggesting
an valid solution!

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/fixtures/email_address.yml

@@ -276,4 +276,12 @@
   email: user2-2@example.com
   lower_email: user2-2@example.com
   is_activated: false
-  is_primary: false
+  is_primary: false
+
+-
+  id: 36
+  uid: 36
+  email: abcde@gitea.com
+  lower_email: abcde@gitea.com
+  is_activated: true
+  is_primary: false

models/fixtures/gpg_key.yml

@@ -1 +1,23 @@
-[] # empty
+-
+  id: 5
+  owner_id: 36
+  key_id: B15431642629B826
+  primary_key_id:
+  content: 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
+  verified: true
+  can_sign: true
+  can_encrypt_comms: true
+  can_encrypt_storage: true
+  can_certify: true
+
+-
+  id: 6
+  owner_id: 36
+  key_id: EE3AF48454AFD619
+  primary_key_id: B15431642629B826
+  content: zsDNBGTrY3UBDADsHrzuOicQaPdUQm0+0UNrs92cESm/j/4yBBUk+sfLZAo6J99c4eh4nAQzzZ7al080rYKB0G+7xoRz1eHcQH6zrVcqB8KYtf/sdY47WaMiMyxM+kTSvzp7tsv7QuSQZ0neUEXRyYMz5ttBfIjWUd+3NDItuHyB+MtNWlS3zXgaUbe5VifqKaNmzN0Ye4yXTKcpypE3AOqPVz+iIFv3c6TmsqLHJaR4VoicCleAqLyF/28WsJO7M9dDW+EM3MZVnsVpycTURyHAJGfSk10waQZAaRwmarCN/q0KEJ+aEAK/SRliUneBZoMO5hY5iBeG432tofwaQqAahPv9uXIb1n2JEMKwnMlMA9UGD1AcDbywfj1m/ZGBBw95i4Ekkfn43RvV3THr7uJU/dRqqP+iic4MwpUrOxqELW/kmeHXlBcNbZZhEEvwRoW7U2/9eeuog4nRleRJ0pi/xOP9wmxkKjaIPIK3phdBtEpVk4w/UTAWNdyIIrFggukeAnZFyGJwlm8AEQEAAQ==
+  verified: true
+  can_sign: true
+  can_encrypt_comms: true
+  can_encrypt_storage: true
+  can_certify: true

models/fixtures/user.yml

@@ -1301,7 +1301,7 @@
   lower_name: limited_org36
   name: limited_org36
   full_name: Limited Org 36
-  email: limited_org36@example.com
+  email: abcde@gitea.com
   keep_email_private: false
   email_notifications_preference: enabled
   passwd: ZogKvWdyEx:password
@@ -1320,7 +1320,7 @@
   allow_create_organization: true
   prohibit_login: false
   avatar: avatar22
-  avatar_email: limited_org36@example.com
+  avatar_email: abcde@gitea.com
   use_custom_avatar: false
   num_followers: 0
   num_following: 0