Add yamllint checks (#7424)

.github/FUNDING.yml

@@ -1 +1,2 @@
+---
 custom: https://lmms.io/get-involved/#donate

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -78,7 +78,8 @@ body:
       label: Screenshots / Minimum Reproducible Project
       description: |
         - Upload any screenshots showing the bug in action.
-        - If possible, also include a .mmp/.mmpz project containing the simplest possible setup needed to reproduce the bug.
+        - If possible, also include a .mmp/.mmpz project containing the simplest possible
+          setup needed to reproduce the bug.
 
         ***Note:** To upload a project file to GitHub, it will need to be placed in a .zip archive.*
   - type: checkboxes

.github/ISSUE_TEMPLATE/config.yml

@@ -1,4 +1,5 @@
+---
 contact_links:
-- name: Get help on Discord
-  url: https://lmms.io/chat/
-  about: Need help? Have a question? Reach out to other LMMS users on our Discord server!
+  - name: Get help on Discord
+    url: https://lmms.io/chat/
+    about: Need help? Have a question? Reach out to other LMMS users on our Discord server!

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -10,7 +10,8 @@ body:
       label: Enhancement Summary
       description: |
         - Briefly describe the enhancement.
-        - Explain why you believe the proposed enhancement to be a good idea, and (if applicable) how it helps overcome a limitation of LMMS you are currently facing.
+        - Explain why you believe the proposed enhancement to be a good idea, and (if applicable) how it helps
+          overcome a limitation of LMMS you are currently facing.
     validations:
       required: true
   - type: textarea

.github/no-response.yml

@@ -1,2 +1,3 @@
+---
 # Label requiring a response
 responseRequiredLabel: "response required"

.github/workflows/build.yml

@@ -260,12 +260,14 @@ jobs:
       - name: Cache ccache data
         uses: actions/cache@v3
         with:
+          # yamllint disable rule:line-length
           key: "ccache-${{ github.job }}-${{ matrix.arch }}-${{ github.ref }}\
             -${{ github.run_id }}"
           restore-keys: |
             ccache-${{ github.job }}-${{ matrix.arch }}-${{ github.ref }}-
             ccache-${{ github.job }}-${{ matrix.arch }}-
           path: ~\AppData\Local\ccache
+          # yamllint enable rule:line-length
       - name: Install tools
         run: choco install ccache
       - name: Install Qt

.github/workflows/checks.yml

@@ -31,3 +31,10 @@ jobs:
             $(find "./cmake/" -type f -name '*.sh' -o -name "*.sh.in") \
             doc/bash-completion/lmms \
             buildtools/update_locales
+  yamllint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out
+        uses: actions/checkout@v3
+      - name: Run yamllint
+        run: for i in $(git ls-files '*.yml'); do yamllint $i; done

.yamllint

@@ -0,0 +1,3 @@
+rules:
+  line-length:
+    max: 120  # be conforming to LMMS coding rules