Update heroku/buildpacks-python to v0.21.0 (#626)

## heroku/python

### Changed

- The build now fails early if known problematic Python and pip-related env vars have been set by the user or earlier buildpacks. ([#308](heroku/buildpacks-python#308))
- The `PIP_PYTHON` env var is now only set at build time. ([#307](heroku/buildpacks-python#307))

### Removed

- Stopped setting the `LANG` env var. ([#306](heroku/buildpacks-python#306))
- Stopped setting the `PYTHONHOME` env var. ([#309](heroku/buildpacks-python#309))

Co-authored-by: heroku-linguist[bot] <136119646+heroku-linguist[bot]@users.noreply.github.com>

builder-20/builder.toml

@@ -43,7 +43,7 @@ version = "0.20.5"
 
 [[buildpacks]]
   id = "heroku/python"
-  uri = "docker://docker.io/heroku/buildpack-python@sha256:96483f20b7bd00d638314440729dda93c693ec49abe36cace853e6878cb5bd78"
+  uri = "docker://docker.io/heroku/buildpack-python@sha256:793110da0466bba54dd5da229e8ede949fd156da383c33cd5304d963d0520777"
 
 [[buildpacks]]
   id = "heroku/ruby"
@@ -56,7 +56,7 @@ version = "0.20.5"
 [[order]]
   [[order.group]]
     id = "heroku/python"
-    version = "0.20.1"
+    version = "0.21.0"
   [[order.group]]
     id = "heroku/procfile"
     version = "3.1.2"

builder-22/builder.toml

@@ -47,7 +47,7 @@ version = "0.20.5"
 
 [[buildpacks]]
   id = "heroku/python"
-  uri = "docker://docker.io/heroku/buildpack-python@sha256:96483f20b7bd00d638314440729dda93c693ec49abe36cace853e6878cb5bd78"
+  uri = "docker://docker.io/heroku/buildpack-python@sha256:793110da0466bba54dd5da229e8ede949fd156da383c33cd5304d963d0520777"
 
 [[buildpacks]]
   id = "heroku/ruby"
@@ -64,7 +64,7 @@ version = "0.20.5"
     optional = true
   [[order.group]]
     id = "heroku/python"
-    version = "0.20.1"
+    version = "0.21.0"
   [[order.group]]
     id = "heroku/procfile"
     version = "3.1.2"

builder-24/builder.toml

@@ -47,7 +47,7 @@ mirrors = ["public.ecr.aws/heroku/heroku:24"]
 
 [[buildpacks]]
   id = "heroku/python"
-  uri = "docker://docker.io/heroku/buildpack-python@sha256:96483f20b7bd00d638314440729dda93c693ec49abe36cace853e6878cb5bd78"
+  uri = "docker://docker.io/heroku/buildpack-python@sha256:793110da0466bba54dd5da229e8ede949fd156da383c33cd5304d963d0520777"
 
 [[buildpacks]]
   id = "heroku/ruby"
@@ -64,7 +64,7 @@ mirrors = ["public.ecr.aws/heroku/heroku:24"]
     optional = true
   [[order.group]]
     id = "heroku/python"
-    version = "0.20.1"
+    version = "0.21.0"
   [[order.group]]
     id = "heroku/procfile"
     version = "3.1.2"