CI: Use anaconda-client v1.10.0 for upload

As anaconda-client is no longer supported with pip then all modern
installations must be done with conda or mamba. To make this process
simple, use the mamba-org/provision-with-micromamba GitHub Action
and have it only install anaconda-client=1.10.0. The GitHub Action
will additionally print out the environment information which is useful
for reproducibility and debugging information.
   - c.f. https://github.com/Anaconda-Platform/anaconda-client/ Issue 618
   - c.f. https://github.com/mamba-org/provision-with-micromamba

The option `channels: main` is required to be used as anaconda-client
is currently only maintained on the "main" channel.
   - c.f. https://anaconda.org/main/anaconda-client

The default shell is also set to `bash -l {0}` throughout the workflow
to ensure that micromamba can be loaded properly once it is setup.
   - c.f. https://github.com/mamba-org/provision-with-micromamba/blob/34071ca7df4983ccd272ed0d3625818b27b70dcc/README.md#important

Author: matthewfeickert

.github/workflows/nightlies.yml

@@ -11,17 +11,14 @@ jobs:
   upload_nightly_wheels:
     name: Upload nightly wheels to Anaconda Cloud
     runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash -l {0}
     if: github.repository_owner == 'matplotlib'
 
     steps:
-      - name: Install Python
-        uses: actions/setup-python@v4
-        with:
-          python-version: '3.x'
-
       # c.f. https://github.com/actions/download-artifact/issues/3#issuecomment-1017141067
       - name: Download wheel artifacts from last build on 'main'
-        shell: bash
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
@@ -50,12 +47,14 @@ jobs:
           mv *.whl dist/
           ls -l dist/
 
+        # N.B. anaconda-client is only maintained on the main channel
       - name: Install anaconda-client
-        run: |
-          python -m pip install --upgrade pip setuptools wheel
-          # c.f. https://github.com/Anaconda-Platform/anaconda-client/issues/540
-          python -m pip install git+https://github.com/Anaconda-Server/anaconda-client@be1e14936a8e947da94d026c990715f0596d7043
-          python -m pip list
+        uses: mamba-org/provision-with-micromamba@v12
+        with:
+          environment-file: false
+          environment-name: nightlies
+          extra-specs: anaconda-client=1.10.0
+          channels: main
 
       - name: Upload wheels to Anaconda Cloud as nightlies
         run: |
@@ -65,7 +64,6 @@ jobs:
             dist/matplotlib-*.whl
 
       - name: Remove old uploads to save space
-        shell: bash
         run: |
           N_LATEST_UPLOADS=5