Update repositories.txt (#6964)

MISTERNEGATIVE21 · web-flow · commit 1917a9ddaf6d · 2025-09-19T08:06:13.000Z
Added  QuectelEC200U_CN - Arduino library for Quectel EC200U (CN-AA)
diff --git a/repositories.txt b/repositories.txt
@@ -8418,3 +8418,4 @@ https://github.com/stm32duino/IIS2DULPX
 https://github.com/stm32duino/ISM330IS
 https://github.com/stm32duino/ILPS22QS
 https://github.com/fulda1/SUSI2
+https://github.com/MISTERNEGATIVE21/QuectelEC200U_CN
