RFR: 8290000: Bump macOS GitHub actions to macOS 11 [v4]

[George Adams]

> macOS 10.15 has been deprecated for some time and will be removed completely on August 30th. See https://github.com/actions/virtual-environments#available-environments and https://github.com/actions/virtual-environments/issues/5583 for context.
> 
> It's also worth pointing out that they are shutting down the agents already which means that we likely see longer wait times for executors so this should speed up the workflow for developers. We'll need to backport this all the way down to JDK8u to avoid breaking the CI system.

George Adams has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  switch to macos-11 as 12 doesn't have toolchain

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9426/files
  - new: https://git.openjdk.org/jdk/pull/9426/files/d65f5d06..bbb2758d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9426&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9426&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9426.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9426/head:pull/9426

PR: https://git.openjdk.org/jdk/pull/9426