gistfile1.txt

See the difference between executing
Using label sutaakar:7.67.x-JBPM-10042 -> 1 result

curl -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/kiegroup/droolsjbpm-integration/pulls?head=sutaakar:7.67.x-JBPM-10042  | jq length
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 21389    0 21389    0     0  49283      0 --:--:-- --:--:-- --:--:-- 49170
1

Using ref 7.67.x-JBPM-10042 -> 30 results (the default per_page value) (and the are no 30 elements with 7.67.x-JBPM-10042 ref)

curl -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/kiegroup/droolsjbpm-integration/pulls?head=7.67.x-JBPM-10042  | jq length
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  620k    0  620k    0     0   467k      0 --:--:--  0:00:01 --:--:--  467k
30

same result in case I user whatever

curl -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/kiegroup/droolsjbpm-integration/pulls?head=whatever  | jq length
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  620k    0  620k    0     0   473k      0 --:--:--  0:00:01 --:--:--  473k
30

So the problem for grgrzybek:ggrzybek-test-PR still persists (probably because it has been renamed, but this something I can only speculate with without checking your code), see

curl -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/kiegroup/droolsjbpm-integration/pulls?head=grgrzybek:ggrzybek-test-PR  | jq length
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100     5  100     5    0     0     15      0 --:--:-- --:--:-- --:--:--    15
0