fix: Use mamba in mulled-build

Author: mbargull

bioconda_utils/involucro

@@ -2,4 +2,5 @@
 
 exec involucro \
     -set POSTINSTALL='create-env --conda=: /usr/local' \
+    -set PREINSTALL='conda() { mamba "${@}" ; }' \
     "${@}"

bioconda_utils/pkg_test.py

@@ -159,6 +159,8 @@ def test_package(
     # galaxy-lib always downloads involucro, unless it's in cwd or its path is explicitly given.
     # We inject a POSTINSTALL to the involucro command with a small wrapper to
     # create activation / entrypoint scripts for the container.
+    # We also inject a PREINSTALL to alias conda to mamba so `mamba install` is
+    # used instead of `conda install` in the container builds.
     involucro_path = os.path.join(os.path.dirname(__file__), 'involucro')
     if not os.path.exists(involucro_path):
         raise RuntimeError('internal involucro wrapper missing')