ci: fix bug with script cwd

Created by: jhchabran

This fixes a bug with the moved script, the CWD code wasn't updated.

Test plan

Tested the path locally (set -e was disabled to allow running the command up to the faulty dir change)

Before:

~/work/sourcegraph U devx/fix-logs-uploading $ ./enterprise/dev/ci/scripts/upload-build-logs.sh
./enterprise/dev/ci/scripts/upload-build-logs.sh: line 21: /root/.profile: No such file or directory
--- :go: Building sg
+ pushd dev/sg
./enterprise/dev/ci/scripts/upload-build-logs.sh: line 30: pushd: dev/sg: No such file or directory
+ go build -o ../../sg -ldflags '-X main.BuildCommit=' -mod=mod .
no Go files in /Users/tech/work/sourcegraph/enterprise/dev
+ popd
./enterprise/dev/ci/scripts/upload-build-logs.sh: line 32: popd: directory stack empty
--- :file_cabinet: Uploading logs

After:

~/work/sourcegraph U devx/fix-logs-uploading $ ./enterprise/dev/ci/scripts/upload-build-logs.sh
./enterprise/dev/ci/scripts/upload-build-logs.sh: line 21: /root/.profile: No such file or directory
--- :go: Building sg
+ pushd dev/sg
~/work/sourcegraph/dev/sg ~/work/sourcegraph
+ go build -o ../../sg -ldflags '-X main.BuildCommit=' -mod=mod .
+ popd
~/work/sourcegraph

It's building sg properly, so the path is correct.