fix(ci): downgrade crates requiring rust 1.66 (#7788)

.github/workflows/test-core.yml

@@ -102,6 +102,8 @@ jobs:
         # The --precise flag can only be used once per invocation.
         run: |
           cargo update -p time --precise 0.3.23
+          cargo update -p toml@0.7.7 --precise 0.7.6
+          cargo update -p toml_edit@0.19.15 --precise 0.19.14
 
       - name: test
         uses: actions-rs/cargo@v1