Skip target in taplo checks (#14747)

`target` can contain arbitrary files. Contents depend on tools used and
tests run, and may even include `Cargo.toml` files that are not properly
formatted. The taplo check should never complain on files that are not
meant to be part of the repository, and `target` contents clearly falls
into that category.

`trybuild` is an example of a tool that creates cargo files inside
target directory.

taplo.toml

@@ -18,6 +18,7 @@
 ## https://taplo.tamasfe.dev/configuration/file.html
 
 include = ["**/Cargo.toml"]
+exclude = ["target/*"]
 
 [formatting]
 # Align consecutive entries vertically.