[server] always use . for image builder checkoutLocation

[iQQBot]

Description

all preview environment can't build image, this is because

gitpod/components/server/src/workspace/workspace-starter.ts

Lines 721 to 735 in 45f13cf

	let checkoutLocation =
	(CommitContext.is(workspace.context) && workspace.context.checkoutLocation) || ".";
	if (
	!AdditionalContentContext.hasDockerConfig(workspace.context, workspace.config) &&
	imgsrc.dockerFileSource
	) {
	// TODO(se): we cannot change this initializer structure now because it is part of how baserefs are computed in image-builder.
	// Image builds should however just use the initialization if the workspace they are running for (i.e. the one from above).
	const { initializer, disposable } = await this.createCommitInitializer(
	{ span },
	workspace,
	{
	...imgsrc.dockerFileSource,
	checkoutLocation: ".",

L721 using workspace.context.checkoutLocation and L735 is .

In image build stage we don't care checkoutLocation, this PR always use . for checkoutLocation

Related Issue(s)

Fixes #

How to test

1. start a workspace which need image build, like https://github.com/iQQBot/test.test you will see image builder is work
2. and start another workspace check everything is like before

Release Notes

Fixes image builder not work

Documentation

[geropl]

@iQQBot I will have a look later today if no one else gets around to do so.
Please have a look at this as well.

• Support for multi-repo projects #7785 (comment)
• Support for multi-repo projects #7785 (comment)

[geropl]

Superseded by #8854