test: make upgrade tests pass despite warnings

For a reason I do not entirely understand, the upgrade test started
failing when I removed `rust-toolchain` from the **current** git, even
though old releases still have it. The failures are due to warnings.
Work around this by removing the `#![deny(...)]` and `#[deny(...)]`
lines from the source of the old releases.

Signed-off-by: Lars Wirzenius <liw@liw.fi>

ci-broker.md

@@ -2442,7 +2442,8 @@ export SRCDIR="$CARGO_MANIFEST_DIR"
 	cd ci-broker
 
 	# Build source code.
-	cargo build --all-targets -q
+    find -name '*.rs' -exec sed -Ei '/\[deny\(/d' '{}' +
+    cargo build --all-targets
 
     (echo "Old CI run lists:"
 	cargo run -q --bin cibtool -- --db "$db" run list 1>&2