Use auto-activate instead of the deprecated auto-activate-base (#172)

setup-miniconda v4 warns on every run:

  `auto-activate-base` is deprecated. Please use `auto-activate`.

Rename the input in ci.yml, cache.yml and publish.yml. The value stays
true, and the installer's default environment is base, so the second
half of the warning (add `activate-environment: base`) does not apply;
each job still activates the quantecon environment.


Claude-Session: https://claude.ai/code/session_01Wyb6EzbNzY5a8uuJPnDtUb

Co-authored-by: Claude <noreply@anthropic.com>

Author: mmcky

.github/workflows/cache.yml

@@ -12,7 +12,7 @@ jobs:
         uses: conda-incubator/setup-miniconda@v4
         with:
           auto-update-conda: true
-          auto-activate-base: true
+          auto-activate: true
           miniconda-version: 'latest'
           python-version: "3.13"
           environment-file: environment.yml

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
         uses: conda-incubator/setup-miniconda@v4
         with:
           auto-update-conda: true
-          auto-activate-base: true
+          auto-activate: true
           miniconda-version: 'latest'
           python-version: "3.13"
           environment-file: environment.yml

.github/workflows/publish.yml

@@ -16,7 +16,7 @@ jobs:
         uses: conda-incubator/setup-miniconda@v4
         with:
           auto-update-conda: true
-          auto-activate-base: true
+          auto-activate: true
           miniconda-version: 'latest'
           python-version: "3.13"
           environment-file: environment.yml