Update common github actions (#3119)

Signed-off-by: Knative Automation <[email protected]>

Author: knative-automation

.github/workflows/knative-releasability.yaml

@@ -36,8 +36,8 @@ jobs:
     env:
       #########################################
       #   Update this section each release.   #
-      RELEASE: 'v0.19'
-      SLACK_CHANNEL: 'release-19'
+      RELEASE: 'v0.20'
+      SLACK_CHANNEL: 'release-20'
       #########################################
 
     steps:

.github/workflows/knative-verify.yaml

@@ -45,7 +45,9 @@ jobs:
 
     - name: Install Dependencies
       run: |
-        go get github.com/google/ko/cmd/ko
+        curl -L https://github.com/google/ko/releases/download/v0.6.0/ko_0.6.0_Linux_x86_64.tar.gz | tar xzf - ko
+        chmod +x ./ko
+        sudo mv ko /usr/local/bin
         go get github.com/google/go-licenses
 
     - name: Check out code onto GOPATH