Faster and more concise way of adding headers (#5213)

* Faster and more concise way of adding headers

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fixed issue with the last line

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

translate/storage/poheader.py

@@ -460,10 +460,12 @@ def makeheader(self, **kwargs):
         headerpo._store = self
         headerpo.markfuzzy()
         headeritems = self.makeheaderdict(**kwargs)
-        headervalue = ""
-        for key, value in headeritems.items():
-            if value is None:
-                continue
-            headervalue += f"{key}: {value}\n"
+        headervalue = "".join(
+            [
+                f"{key}: {value}\n"
+                for key, value in headeritems.items()
+                if value is not None
+            ]
+        )
         headerpo.target = headervalue
         return headerpo