v4.2.0-rc1

No breaking changes so far since v4.1.0.

What's Changed

• Add new issue templates by @mhuisi in #2519
• chore: begin development cycle for 4.2.0 by @semorrison in #2545
• chore: do not generate PR releases from forks by @semorrison in #2550
• chore: when bumping Mathlib testing branches, bump to latest nightly-testing by @semorrison in #2553
• fix: uninterpolated error message in registerRpcProcedure by @thorimur in #2547
• Enforce linebreak between calc steps by @Kha in #2532
• fix: rename parameter of withImportModules to match doc string by @dwrensha in #2530
• perf: reduce allocations in unused variable linter by @hargoniX in #2491
• fix: set MACOSX_DEPLOYMENT_TARGET in CI only by @Kha in #2556
• CI: label stale PRs by @Kha in #2561
• chore: disambiguate whnf system category by @Kha in #2560
• fix: use MoveFileEx for rename on win by @digama0 in #2546
• fix: set ref in getCalcFirstStep by @PatrickMassot in #2563
• perf: Use flat ByteArrays in Trie by @nomeata in #2529
• chore: update domain by @Kha in #2566
• feat: lake: add name to manifest by @tydeu in #2565
• fix: only return new mvars from refine, elabTermWithHoles, and withCollectingNewGoalsFrom by @thorimur in #2502
• fix: don't try to generate below for nested predicates. by @arthur-adjedj in #2390
• perf: do not detect lean's toolchain by @tydeu in #2570
• test: add lake benchmarks by @tydeu in #2457
• perf: lake: build lakefile environments incrementally by @Kha in #2573
• perf: lake: no lean --githash when collocated by @tydeu in #2572
• test: lake: add env & dep cfg benchmarks + cleanup by @tydeu in #2574

Full Changelog: v4.1.0...v4.2.0-rc1