Pin the nightly version in CI

[gregtatum]

This is part of the work for #374. I have several PRs with red CI. I'm keeping this as draft while I work on it.

[jira-pull-request-webhook]

Notice: the branch changed across the force-push!

• .github/workflows/build-test.yml is different
• .github/workflows/coverage.yml is different

View Diff Across Force-Push

~ Your Friendly Jira-GitHub PR Checker Bot

[jira-pull-request-webhook]

Notice: the branch changed across the force-push!

• .github/workflows/build-test.yml is different
• .github/workflows/coverage.yml is different

View Diff Across Force-Push

~ Your Friendly Jira-GitHub PR Checker Bot

[sffc]

Why are you picking such old versions of nightly? Seems like you should pick the most recent version that works (something in 2021, not 2020)

[coveralls]

Pull Request Test Coverage Report for Build 5291fb1cbf8150748879d2002bd5bebdddc23e68-PR-526

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 10 unchanged lines in 9 files lost coverage.
• Overall coverage increased (+0.04%) to 72.75%

---

Files with Coverage Reduction	New Missed Lines	%
components/datetime/src/mock.rs	1	65.08%
components/locid/src/helpers.rs	1	92.59%
components/plurals/src/rules/serializer.rs	1	62.04%
components/provider_cldr/src/reader.rs	1	93.75%
components/provider_fs/src/deserializer.rs	1	41.67%
components/provider/src/error.rs	1	0%
components/provider/src/resource.rs	1	81.22%
resources/testdata/src/test_data_provider.rs	1	60.0%
components/datetime/src/provider/helpers.rs	2	57.73%

Totals
Change from base Build b15c0b36901095406a67e3620a3d1d0e294b7692:	0.04%
Covered Lines:	4859
Relevant Lines:	6679

---

💛 - Coveralls

[sffc]

Closer! Coverage is working now, but Memory is still broken:

     Running `target/debug/icu_benchmark_memory --os ubuntu-latest icu_datetime/work_log icu_locid/syntatically_canonicalize_locales icu_locid/filter_langids icu_plurals/unread_emails icu_plurals/elevator_floors icu_uniset/unicode_bmp_blocks_selector fixed_decimal/permyriad writeable/writeable_message`
[memory] Starting example "work_log"
[memory] > error: toolchain 'nightly-x86_64-unknown-linux-gnu' is not installed
The example "work_log" had a non-zero exit code: 1
Error: Process completed with exit code 1.

[sffc]

Now that the P0 issue has been fixed (by #529), should we use this PR to pin the version of Rust in both nightly and stable CI builds? And then hopefully unblock adding back CI caching?

[gregtatum]

I'm going to go ahead and mark this as ready for review, as the only outstanding CI failure is from:

PR #518
https://github.com/unicode-org/icu4x/runs/2040894278

[sffc]

RSLGTM for the nightly toolchain version. As discussed, we should follow up with a PR to pin the stable version as well.