GHA: add yamlcheck

Uses `yamllint`.

Also:
- fix warning for existing YAML files:
  ```
  [truthy] truthy value should be one of [false, true]
  ```

Closes #14650

.github/workflows/appveyor-status.yml

@@ -4,7 +4,7 @@
 
 name: AppVeyor Status Report
 
-on:
+'on':
   status
 
 concurrency:

.github/workflows/awslc.yml

@@ -4,7 +4,7 @@
 
 name: Linux AWS-LC
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/checkdocs.yml

@@ -7,7 +7,7 @@
 
 name: Docs
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/checksrc.yml

@@ -6,7 +6,7 @@
 
 name: Source
 
-on:
+'on':
   push:
     branches:
       - master
@@ -84,6 +84,9 @@ jobs:
       - name: spacecheck
         run: .github/scripts/spacecheck.pl
 
+      - name: yamlcheck
+        run: .github/scripts/yamlcheck.sh
+
       - name: binarycheck
         run: .github/scripts/binarycheck.pl
 

.github/workflows/codeql-analysis.yml

@@ -4,7 +4,7 @@
 
 name: CodeQL
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/configure-vs-cmake.yml

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: curl
 
 name: configure-vs-cmake
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/curl-for-win.yml

@@ -4,7 +4,7 @@
 ---
 name: curl-for-win
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/cygwin.yml

@@ -4,7 +4,7 @@
 
 name: Cygwin
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/distcheck.yml

@@ -4,7 +4,7 @@
 
 name: dist
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/fuzz.yml

@@ -4,7 +4,7 @@
 
 name: Fuzzer
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/hacktoberfest-accepted.yml

@@ -4,7 +4,7 @@
 
 name: Hacktoberfest
 
-on:
+'on':
   # this must not ever run on any other branch than master
   push:
     branches:

.github/workflows/http3-linux.yml

@@ -4,7 +4,7 @@
 
 name: http3-linux
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/label.yml

@@ -10,7 +10,7 @@
 # https://github.com/actions/labeler
 
 name: Labeler
-on: [pull_request_target]
+'on': [pull_request_target]
 
 jobs:
   label:

.github/workflows/linux-old.yml

@@ -18,7 +18,7 @@
 
 name: Old Linux
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/linux.yml

@@ -4,7 +4,7 @@
 
 name: Linux
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/linux32.yml

@@ -4,7 +4,7 @@
 
 name: Linux 32-bit
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/macos.yml

@@ -4,7 +4,7 @@
 
 name: macOS
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/non-native.yml

@@ -4,7 +4,7 @@
 
 name: non-native
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/torture.yml

@@ -4,7 +4,7 @@
 
 name: Linux torture
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/windows.yml

@@ -4,7 +4,7 @@
 
 name: Windows
 
-on:
+'on':
   push:
     branches:
       - master

.github/workflows/wolfssl.yml

@@ -4,7 +4,7 @@
 
 name: Linux wolfSSL
 
-on:
+'on':
   push:
     branches:
       - master