Verify git checkout path is in site directory

[QuLogic]

This is unlikely, as we verify inputs come from GitHub using signatures, but it's best to be safe about this.

[lgtm-com]

This pull request introduces 1 alert when merging 080a29c into 61de8b0 - view on LGTM.com

new alerts:

• 1 for Uncontrolled data used in path expression

[lgtm-com]

This pull request introduces 1 alert when merging c3b7a7a into 61de8b0 - view on LGTM.com

new alerts:

• 1 for Uncontrolled data used in path expression

[lgtm-com]

This pull request introduces 1 alert when merging 518ac57 into 79993d7 - view on LGTM.com

new alerts:

• 1 for Uncontrolled data used in path expression

[tacaswell]

In the right fix here to hard-code the repo we expect and launder it through a dictionary lookup?

[QuLogic]

So looking at it closer, I think it's impossible to break out. We check that repo == repository, where one is the path given in the webhook, and the other is the request URL fragment. The latter cannot go up because aiohttp normalizes the URL, and it would not trigger the request handler.

I also think that LGTM and CodeQL are not correctly understanding pathlib, but I can open an issue there for that separately.

[lgtm-com]

This pull request fixes 1 alert when merging a52631a into 79993d7 - view on LGTM.com

fixed alerts:

• 1 for Uncontrolled data used in path expression