Pin once_cell version to MSRV (#72)

Author: kirillsemyonkin

.github/dependabot.yml

@@ -1,12 +1,16 @@
----
-version: 2
-updates:
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-
-  - package-ecosystem: "cargo"
-    directory: "/"
-    schedule:
-      interval: "weekly"
+---
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+
+  - package-ecosystem: "cargo"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    ignore:
+      # stay on rust msrv
+      - dependency-name: "trybuild"
+      - dependency-name: "once_cell"

implicit-clone-derive/Cargo.toml

@@ -22,4 +22,5 @@ syn = { version = "2", features = ["full"] }
 [dev-dependencies]
 implicit-clone = { path = ".." }
 trybuild = "=1.0.89"
+once_cell = "=1.9" # stay on rust 1.65
 rustversion = "1"