infra: set github actions max-parallel to 15 (#3057)

this is the guidance from apache infra, see
https://s.apache.org/max-parallel
* All workflows MUST have a job concurrency level less than or equal to
20. This means a workflow cannot have more than 20 jobs running at the
same time across all matrices.
* All workflows SHOULD have a job concurrency level less than or equal
to 15. Just because 20 is the max, doesn't mean you should strive for
20.

note that `max-parallel` limits the number of simultaneous runs ([see
docs](https://docs.github.com/en/actions/how-tos/write-workflows/choose-what-workflows-do/run-job-variations#defining-the-maximum-number-of-concurrent-jobs)),
other jobs will just wait

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: kevinjqliu <9057843+kevinjqliu@users.noreply.github.com>

Author: kevinjqliu

.github/workflows/pypi-build-artifacts.yml

@@ -31,6 +31,7 @@ jobs:
     name: Build artifacts for PyPi on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
+      max-parallel: 15
       matrix:
         os: [ ubuntu-latest, ubuntu-24.04-arm, windows-latest, macos-15-intel, macos-latest ]
 

.github/workflows/python-ci.yml

@@ -46,6 +46,7 @@ jobs:
   lint-and-unit-test:
     runs-on: ubuntu-latest
     strategy:
+      max-parallel: 15
       fail-fast: true
       matrix:
         python: ['3.10', '3.11', '3.12', '3.13']

.github/workflows/svn-build-artifacts.yml

@@ -31,6 +31,7 @@ jobs:
     name: Build artifacts for SVN on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
+      max-parallel: 15
       matrix:
         os: [ ubuntu-latest, ubuntu-24.04-arm, windows-latest, macos-15-intel, macos-latest ]