[Chapel Merge] Update `ubuntu-latest` runners to `ubuntu-26.04` now

Branch: refs/heads/main
Revision: 2aa4f0cbacf126428bcbf1bd924234865fba84c5
Author: arifthpe
Link: Update `ubuntu-latest` runners to `ubuntu-26.04` now by arifthpe · Pull Request #29452 · chapel-lang/chapel · GitHub
Log Message:
Update ubuntu-latest runners to ubuntu-26.04 now (#29452)

Temporarily change our ubuntu-latest GA runners to point to
ubuntu-26.04, opting in ahead of their update to refer to
ubuntu-26.04 in about a month so we can work out the kinks now.

Once validated, this should be reverted to ubuntu-latest so we get
26.04 and future updates automatically.

[skipping review, discussed off-thread]

Compare: Comparing 0350468ff2228a94ec7bc433c5ee94bddbe2195e...08637b592694852ac221ba4278e8c7c2abaa1f26 · chapel-lang/chapel · GitHub

Diff:
M .github/workflows/arkouda-smoke-test.yml
M .github/workflows/build-CI-container.yml
M .github/workflows/core-ci-checks.yml
M .github/workflows/docker-image-builds.yml
M .github/workflows/extended-ci-checks.yml
M .github/workflows/full-ci-checks.yml
M .github/workflows/ga-paratest.yml
M .github/workflows/lint-workflows.yml
M .github/workflows/package-builds.yml
M .github/workflows/release-docker.yml
M .github/workflows/release-tarball.yml
https://github.com/chapel-lang/chapel/pull/29452.diff