runner.conda: Bump Micromamba from 1.5.8 → 2.1.0

Newer versions since 2.0.0 include fix for installing
nextstrain/conda-base when the dependencies specify
`x86_64-microarch-level`.

Since we're bumping the version, might has well bump to the latest
version. Skimmed over the mamba CHANGELOG from 1.5.1 to 2.1.0 and
nothing jumped out to me.

Resolves <#429>

Author: joverlee521

CHANGES.md

@@ -58,6 +58,11 @@ our broader "workflows as programs" endeavor.
   that work is being done when checks take a second or two.
   ([#418](https://github.com/nextstrain/cli/pull/418))
 
+* The Conda runtime now uses Micromamba 2.1.0 (upgraded from 1.5.8) to manage
+  the runtime environment. The newer version fixes the installation error for
+  packages that include the `_x86_64-microarch-level` virtual package dependency.
+  ([#430](https://github.com/nextstrain/cli/pull/430))
+
 
 # 9.0.0 (24 March 2025)
 

nextstrain/cli/runner/conda.py

@@ -67,7 +67,7 @@
     <https://anaconda.org/conda-forge/micromamba/>`__, or the special string
     ``latest``.
 
-    Defaults to ``1.5.8``.
+    Defaults to ``2.1.0``.
 """
 
 import json
@@ -100,7 +100,7 @@
 
 # If you update the version pin below, please update the docstring above too.
 MICROMAMBA_VERSION = os.environ.get("NEXTSTRAIN_CONDA_MICROMAMBA_VERSION") \
-                  or "1.5.8"
+                  or "2.1.0"
 
 NEXTSTRAIN_CHANNEL = os.environ.get("NEXTSTRAIN_CONDA_CHANNEL") \
                   or "nextstrain"