ci: downgrade container to 20.04 (#108)

.github/workflows/license.yaml

@@ -8,7 +8,7 @@ on:
     types: [opened, synchronize, reopened, ready_for_review]
 jobs:
   license-header-check:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     name: license-header-check
     steps:
     - uses: actions/checkout@v2

.github/workflows/main.yml

@@ -14,7 +14,7 @@ env:
 jobs:
   typos:
     name: Spell Check with Typos
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - uses: crate-ci/typos@v1.0.4
@@ -22,7 +22,7 @@ jobs:
   check:
     name: Check
     if: github.event.pull_request.draft == false
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@v3
@@ -50,7 +50,7 @@ jobs:
   fmt:
     name: Rustfmt
     if: github.event.pull_request.draft == false
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@v3
@@ -69,7 +69,7 @@ jobs:
   clippy:
     name: Clippy
     if: github.event.pull_request.draft == false
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@v3

.github/workflows/pr-title-checker.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   check:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     timeout-minutes: 10
     steps:
       - uses: thehanimo/pr-title-checker@v1.3.4