fix: make git installation more resilient against ssl tampering

[mhuisi]

This PR makes the installation of Git in the extension more resilient. On a Windows server, I witnessed the following error with the current installation:

Failed when searching source: msstore
An unexpected error occurred while executing the command:
0x8a15005e : The server certificate did not match any of the expected values.

I'm not sure whether this issue is specific to the Windows server, but explicitly setting the source prevents this issue from occurring.