What is the best practice for dealing with passwords in git repositories?

An approach can be to set password (or API key) using an environment variable. So this password is out of revision control.

With Bash, you can set environment variable using

export your_env_variable='your_password'

This approach can be use with continuous integration services like Travis, your code (without password) being stored in a GitHub repository can be executed by Travis (with your password being set using environment variable).

With Bash, you can get value of an environment variable using:

echo "$your_env_variable"

With Python, you can get value of an environment variable using:

import os
print(os.environ['your_env_variable'])

PS: be aware that it's probably a bit risky (but it's a quite common practice) https://www.bleepingcomputer.com/news/security/javascript-packages-caught-stealing-environment-variables/

PS2: this dev.to article titled "How to securely store API keys" may be interesting to read.

The typical way to do this is to read the password info from a configuration file. If your configuration file is called foobar.config, then you would commit a file called foobar.config.example to the repository, containing sample data. To run your program, you would create a local (not tracked) file called foobar.config with your real password data.

To filter out your existing password from previous commits, see the GitHub help page on Removing sensitive data.