ci/update_conda_lock: do not run on PRs

Signed-off-by: Unai Martinez-Corral <umartinezcorral@antmicro.com>

.github/workflows/update_conda_lock.yml

diff --git a/.github/workflows/update_conda_lock.yml b/.github/workflows/update_conda_lock.yml
index 8127af1..a160adb 100644
--- a/.github/workflows/update_conda_lock.yml
+++ b/.github/workflows/update_conda_lock.yml
@@ -2,7 +2,6 @@
 
 on:
   push:
-  pull_request:
   schedule:
     - cron: '0 3 * * *'
   workflow_dispatch: