Run workflows on every PR

.github/workflows/build-gnutls.yml

@@ -4,8 +4,6 @@ on:
     branches:
     - master
   pull_request:
-    branches:
-    - master
 jobs:
   build-linux:
     runs-on: ubuntu-latest

.github/workflows/build-nice.yml

@@ -4,8 +4,6 @@ on:
     branches:
     - master
   pull_request:
-    branches:
-    - master
 jobs:
   build-media:
     runs-on: ubuntu-latest

.github/workflows/build-openssl.yml

@@ -4,8 +4,6 @@ on:
     branches:
     - master
   pull_request:
-    branches:
-    - master
 jobs:
   build-linux:
     runs-on: ubuntu-latest