Skip checking .po file if it's not edited on the current branch

.github/workflows/code-quality.yaml

@@ -59,6 +59,13 @@ jobs:
           linter_env = new.env()
           for (f in list.files('.ci/linters/po', full.names=TRUE)) sys.source(f, linter_env)
           for (po_file in list.files(pattern = "[.]po$", full.names=TRUE)) {
+            # only pay attention to files edited in the current PR, otherwise we can get
+            #   a situation like after #6424 where some untranslated messages were added
+            #   as part of non-translation maintenance, but this GHA would go red repeatedly
+            #   until a translation is added or the blank/fuzzy translations removed. We'd
+            #   rather only have the failure on one PR, then ignore these files later.
+            diff_v_master = system2("git", c("diff", "master", po_file), stdout=TRUE)
+            if (!length(diff_v_master)) next
             for (linter in ls(linter_env)) linter_env[[linter]](po_file)
           }
         shell: Rscript {0}