chore: specify relative path for packages in pandas-gbq noxfile.py (#16746)

Use relative paths instead of cloning the entire repo from github and
stepping into the sub directory which takes a lot of memory and time and
results in the presubmit(s) to timeout.

Author: ohmayr

packages/pandas-gbq/noxfile.py

@@ -362,8 +362,8 @@ def prerelease_deps(session):
     # any potential breaking changes. For context, see:
     # https://github.com/googleapis/google-cloud-python/issues/854
     session.install(
-        "git+https://github.com/googleapis/google-cloud-python.git@main#subdirectory=packages/google-cloud-bigquery",
-        "git+https://github.com/googleapis/google-cloud-python.git@main#subdirectory=packages/google-cloud-bigquery-storage",
+        "../google-cloud-bigquery",
+        "../google-cloud-bigquery-storage",
     )
 
     # Because we test minimum dependency versions on the minimum Python