*: rename master branch to main (external repos)

.cci.jenkinsfile

@@ -1,4 +1,4 @@
-// Documentation: https://github.com/coreos/coreos-ci/blob/master/README-upstream-ci.md
+// Documentation: https://github.com/coreos/coreos-ci/blob/main/README-upstream-ci.md
 
 stage("Build") {
 parallel normal: {

tests/inst/src/destructive.rs

@@ -1,7 +1,7 @@
 //! Test that interrupting an upgrade is safe.
 //!
 //! This test builds on coreos-assembler's "external tests":
-//! https://github.com/coreos/coreos-assembler/blob/master/mantle/kola/README-kola-ext.md
+//! https://github.com/coreos/coreos-assembler/blob/main/mantle/kola/README-kola-ext.md
 //! Key to this in particular is coreos-assembler implementing the Debian autopkgtest reboot API.
 //!
 //! The basic model of this test is: