Auto merge of #28793 - servo:dependabot/cargo/synstructure-0.12.6, r=jdm

Bump synstructure from 0.12.3 to 0.12.6

Bumps [synstructure](https://github.com/mystor/synstructure) from 0.12.3 to 0.12.6.
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Cargo.lock

@@ -6387,9 +6387,9 @@ dependencies = [
 
 [[package]]
 name = "synstructure"
-version = "0.12.3"
+version = "0.12.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "67656ea1dc1b41b1451851562ea232ec2e5a80242139f7e679ceccfb5d61f545"
+checksum = "f36bdaa60a83aca3921b5259d5400cbf5e90fc51931376a9bd4a0eb79aa7210f"
 dependencies = [
  "proc-macro2",
  "quote",