Add weekly scheduled CI runs #3532

Job	Run time
alternative_targets (ubuntu-latest, wasm32-unknown-emscripten)	17s
features_check (ubuntu-latest)	3m 51s
alternative_targets (ubuntu-latest, aarch64-apple-ios)	15s
no_std (ubuntu-latest, thumbv6m-none-eabi)	21s
alternative_targets (ubuntu-latest, aarch64-linux-android)	16s
no_std (ubuntu-latest, x86_64-fortanix-unknown-sgx)	20s
rust_msrv (ubuntu-latest)	53s
test_wasip1 (ubuntu-latest, wasm32-wasip1)	27s
rust_versions (ubuntu-latest, stable)	1m 32s
test_wasm (ubuntu-latest)	26s
rust_versions (ubuntu-latest, beta)	56s
rust_versions (ubuntu-latest, nightly)	53s
timezones (ubuntu-latest, ACST-9:30)	1m 13s
check-docs	22s
timezones (ubuntu-latest, EST4)	1m 13s
timezones (ubuntu-latest, UTC0)	1m 9s
cross-targets (x86_64-unknown-illumos)	58s
cross-tests (ubuntu-latest)	1m 52s
timezones (ubuntu-latest, Asia/Katmandu)	1m 14s
timezones (macos-latest, ACST-9:30)	39s
timezones (macos-latest, EST4)	42s
timezones (macos-latest, UTC0)	46s
timezones (macos-latest, Asia/Katmandu)	57s
timezones (windows-latest, ACST-9:30)	1m 36s
timezones (windows-latest, EST4)	1m 38s
timezones (windows-latest, UTC0)	1m 35s
timezones (windows-latest, Asia/Katmandu)	1m 45s
	28m 6s

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