ci: set explicit workflow permissions

Add explicit permissions for modifying pull requests to labeler and
multi-arch-test-build.

Signed-off-by: George Sapkin <george@sapk.in>

.github/workflows/labeler.yml

@@ -4,6 +4,7 @@ on:
 
 permissions:
   contents: read
+  pull-requests: write
 
 jobs:
   labeler:

.github/workflows/multi-arch-test-build.yml

@@ -3,6 +3,10 @@ name: Test and Build
 on:
   pull_request:
 
+permissions:
+  contents: read
+  pull-requests: write
+
 jobs:
   formalities:
     name: Test Formalities