fix: add rust-toolchain.toml to examples (fixes #2151) #1009

Job	Run time
get-example-changed / Get Example Changed	3s
get-matrix / Get Changed Example Matrix	8s
CI (examples/directives) / Run ci (nightly)	2m 56s
CI (examples/counter) / Run ci (nightly)	2m 52s
CI (examples/counter_url_query) / Run ci (nightly)	2m 25s
CI (examples/counters) / Run ci (nightly)	2m 57s
CI (examples/error_boundary) / Run ci (nightly)	2m 55s
CI (examples/errors_axum) / Run ci (nightly)	6m 32s
CI (examples/fetch) / Run ci (nightly)	2m 20s
CI (examples/hackernews) / Run ci (nightly)	6m 56s
CI (examples/hackernews_axum) / Run ci (nightly)	6m 40s
CI (examples/hackernews_islands_axum) / Run ci (nightly)	4m 5s
CI (examples/js-framework-benchmark) / Run ci (nightly)	2m 48s
CI (examples/parent_child) / Run ci (nightly)	2m 19s
CI (examples/router) / Run ci (nightly)	3m 13s
CI (examples/session_auth_axum) / Run ci (nightly)	7m 35s
CI (examples/slots) / Run ci (nightly)	2m 17s
CI (examples/ssr_modes) / Run ci (nightly)	6m 47s
CI (examples/ssr_modes_axum) / Run ci (nightly)	6m 31s
CI (examples/tailwind_axum) / Run ci (nightly)	7m 45s
CI (examples/tailwind_csr) / Run ci (nightly)	3m 41s
CI (examples/todo_app_sqlite_csr) / Run ci (nightly)	8m 8s
CI (examples/todo_app_sqlite_viz) / Run ci (nightly)	7m 12s
CI (examples/todo_app_sqlite) / Run ci (nightly)	9m 14s
CI (examples/todo_app_sqlite_axum) / Run ci (nightly)	8m 24s
CI (examples/todomvc) / Run ci (nightly)	2m 32s
	1h 59m 15s

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