.gitmodules: Use GitHub mirrors

Change-Id: I8e7ff41bfdc5d301a71123c9afd2e434c152932e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/329952
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Rob Mohr <mohrr@google.com>
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Carlos Chinchilla <cachinchilla@google.com>
diff --git a/.gitmodules b/.gitmodules
index 0db194d..d69f401 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -12,16 +12,16 @@
 	branch = main
 [submodule "third_party/stm32cube_f4/hal_driver"]
 	path = third_party/stm32cube_f4/hal_driver
-	url = https://github.com/STMicroelectronics/stm32f4xx_hal_driver.git
+	url = https://pigweed.googlesource.com/third_party/github/STMicroelectronics/stm32f4xx_hal_driver.git
 [submodule "third_party/stm32cube_f4/cmsis_device"]
 	path = third_party/stm32cube_f4/cmsis_device
-	url = https://github.com/STMicroelectronics/cmsis_device_f4.git
+	url = https://pigweed.googlesource.com/third_party/github/STMicroelectronics/cmsis_device_f4.git
 [submodule "third_party/stm32cube_f4/cmsis_core"]
 	path = third_party/stm32cube_f4/cmsis_core
-	url = https://github.com/STMicroelectronics/cmsis_core.git
+	url = https://pigweed.googlesource.com/third_party/github/STMicroelectronics/cmsis_core.git
 [submodule "third_party/FreeRTOS"]
 	path = third_party/FreeRTOS
-	url = https://github.com/FreeRTOS/FreeRTOS-Kernel
+	url = https://pigweed.googlesource.com/third_party/github/FreeRTOS/FreeRTOS-Kernel
 [submodule "third_party/pico_sdk"]
 	path = third_party/pico_sdk
 	url = https://pigweed.googlesource.com/third_party/github/raspberrypi/pico-sdk