Lock ubuntu versions.

Author: jmjoy

.github/workflows/ci.yaml

@@ -37,14 +37,14 @@ jobs:
     - fmt
     - check-and-test
     - doc
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
         with:
           submodules: 'recursive'
 
   license-check:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
         with:
@@ -59,7 +59,7 @@ jobs:
           config: .github/licenserc.yaml
 
   fmt:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
         with:
@@ -76,12 +76,11 @@ jobs:
         features:
           - ""
           - "--all-features"
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
         with:
           submodules: 'recursive'
-      - run: sudo apt-cache madison protobuf-compiler
       - name: Install protoc
         run: sudo apt-get install -y protobuf-compiler=3.6.1.3-2ubuntu5
       - name: Install Rust toolchain
@@ -94,7 +93,7 @@ jobs:
         run: cargo test --workspace --release ${{ matrix.features }}
 
   doc:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
         with:

.github/workflows/codecov.yaml

@@ -25,7 +25,7 @@ on:
       - 'v*'
 jobs:
   test:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
         with:

.github/workflows/e2e.yml

@@ -27,7 +27,7 @@ on:
 
 jobs:
   e2e-rust:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
         with: