fix: resolve issue where pre-release tests may incorrectly fail

Author: parthea

gapic/templates/noxfile.py.j2

@@ -456,7 +456,8 @@ def prerelease_deps(session, protobuf_implementation):
         session.skip("cpp implementation is not supported in python 3.11+")
 
     # Install all dependencies
-    session.install("-e", ".")
+    # use `--pre` as the pre-release version may have a different set of dependencies
+    session.install("-e", ".", "--pre")
 
     # Install dependencies for the unit test environment
     unit_deps_all = UNIT_TEST_STANDARD_DEPENDENCIES + UNIT_TEST_EXTERNAL_DEPENDENCIES
@@ -549,7 +550,8 @@ def core_deps_from_source(session, protobuf_implementation):
     """
 
     # Install all dependencies
-    session.install("-e", ".")
+    # use `--pre` as the pre-release version may have a different set of dependencies
+    session.install("-e", ".", "--pre")
 
     # Install dependencies for the unit test environment
     unit_deps_all = UNIT_TEST_STANDARD_DEPENDENCIES + UNIT_TEST_EXTERNAL_DEPENDENCIES