Add setup-mako action

.github/actions/setup-mako/README.md

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+# setup-mako
+
+A small composite action to set up the environment for Mako.
+
+It installs poetry and all module dependencies.
+
+## Usage
+
+Add the following steps to your workflow:
+
+```yml
+- name: Checkout Ryujinx-Mako
+  uses: actions/checkout@v3
+  with:
+    repository: Ryujinx/Ryujinx-Mako
+    ref: master
+    path: ".ryujinx-mako"
+
+- name: Setup Ryujinx-Mako
+  uses: .ryujinx-mako/.github/actions/setup-mako
+```
+
+

.github/actions/setup-mako/action.yml

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+name: 'Setup Ryujinx-Mako'
+description: 'Setup the environment for Ryujinx-Mako'
+runs:
+  using: 'composite'
+  steps:
+    - run: pipx install poetry
+      shell: bash
+
+    - run: |
+        cd .ryujinx-mako
+        poetry install --only main
+      shell: bash