Drop obsoleted ci skip checks

https://github.blog/changelog/2021-02-08-github-actions-skip-pull-request-and-push-workflows-with-skip-ci/

.github/workflows/baseruby.yml

@@ -6,7 +6,6 @@ jobs:
   baseruby:
     name: BASERUBY
     runs-on: ubuntu-20.04
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     strategy:
       matrix:
         ruby:

.github/workflows/check_dependencies.yml

@@ -7,7 +7,6 @@ jobs:
         os: [ubuntu-20.04, macos-latest]
       fail-fast: true
     runs-on: ${{ matrix.os }}
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     steps:
       - name: Install libraries
         run: |

.github/workflows/compilers.yml

@@ -157,7 +157,6 @@ jobs:
     name: ${{ matrix.entry.name }}
     runs-on: ubuntu-latest
     container: ghcr.io/ruby/ruby-ci-image:latest
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     steps:
       - run: mkdir build
         working-directory:

.github/workflows/macos.yml

@@ -9,7 +9,6 @@ jobs:
       fail-fast: false
     env:
       GITPULLOPTIONS: --no-tags origin ${{github.ref}}
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     steps:
       - run: mkdir build
         working-directory:

.github/workflows/mingw.yml

@@ -22,7 +22,6 @@ jobs:
       matrix:
         test_task: [ "check" ] # to make job names consistent
       fail-fast: false
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     steps:
       - run: mkdir build
         working-directory:

.github/workflows/mjit.yml

@@ -8,7 +8,6 @@ jobs:
         jit_opts: [ "--jit", "--jit-wait" ]
       fail-fast: false
     runs-on: ubuntu-latest
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     env:
       TESTOPTS: '-q --tty=no'
       RUN_OPTS: '--disable-gems ${{ matrix.jit_opts }} --jit-debug=-ggdb3'

.github/workflows/spec_guards.yml

@@ -6,7 +6,6 @@ jobs:
   rubyspec:
     name: Rubyspec
     runs-on: ubuntu-20.04
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     strategy:
       matrix:
         # Specs from ruby/spec should still run on all supported Ruby versions.

.github/workflows/ubuntu.yml

@@ -26,7 +26,6 @@ jobs:
       GITPULLOPTIONS: --no-tags origin ${{github.ref}}
       RUBY_DEBUG: ci
     runs-on: ${{ matrix.os }}
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     steps:
       - run: mkdir build
         working-directory:

.github/workflows/windows.yml

@@ -13,7 +13,6 @@ jobs:
       GITPULLOPTIONS: --no-tags origin ${{github.ref}}
       VCVARS: C:\Program Files (x86)\Microsoft Visual Studio\${{ matrix.vs }}\Enterprise\VC\Auxiliary\Build\vcvars64.bat
       PATCH: C:\msys64\usr\bin\patch.exe
-    if: "!contains(github.event.head_commit.message, '[ci skip]')"
     steps:
       - run: md build
         working-directory: