build: Pin frappe requirements to ^16.0.0 (#39782)

diff --git a/pyproject.toml b/pyproject.toml
index 604aa44..8a0f12c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -39,3 +39,6 @@
 use_parentheses = true
 ensure_newline_before_comments = true
 indent = "\t"
+
+[tool.bench.frappe-dependencies]
+frappe = ">=16.0.0-dev,<17.0.0"