Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a bug report that matches the one I want to file, without success.

Electron Version

34.0.0

What operating system(s) are you using?

Windows

Operating System Version

Windows 10

What arch are you using?

x64

Last Known Working Electron version

14.2.9

Expected Behavior

All requests that are handled with onHeadersReceived should show modified headers (if they are being modified in the handler)

Actual Behavior

Some requests do not show the modified headers.
Example:

electron.session.defaultSession.webRequest.onHeadersReceived((details, callback) => {
		console.log(details.url, details.responseHeaders);
		if (details.responseHeaders) {
			details.responseHeaders["test"] = ["1"];
		}
		callback({cancel: false, responseHeaders: details.responseHeaders});
	});

I am setting a "test" header to each request
Navigating to google.com does not show the header in the first request:

It does appear in the second request though

Testcase Gist URL

https://gist.github.com/t57ser/b97184b3c8772a8ccf7cb600ceac1202

Additional Information

No response