Trim OTA checksum for whitespace before comparing

The OTA checksum is base64 encoded, whitespaces at the start or end
are not part of the checksum. Simply strip them before comparing.

Fixes: #817

matter_server/server/ota/provider.py

@@ -303,11 +303,12 @@ async def download_update(self, update_desc: dict) -> None:
                 # Download finished, check checksum if necessary
                 if checksum_alg:
                     checksum = b64encode(checksum_alg.digest()).decode("ascii")
-                    if checksum != update_desc["otaChecksum"]:
+                    checksum_expected = update_desc["otaChecksum"].strip()
+                    if checksum != checksum_expected:
                         LOGGER.error(
-                            "Checksum mismatch for file '%s', expected: %s, got: %s",
+                            "Checksum mismatch for file '%s', expected: '%s', got: '%s'",
                             file_name,
-                            update_desc["otaChecksum"],
+                            checksum_expected,
                             checksum,
                         )
                         await loop.run_in_executor(None, file_path.unlink)