refactor(platform): Rename "branchName" to "sourceBranch" (#7284)

lib/platform/azure/__snapshots__/index.spec.ts.snap

lib/platform/azure/__snapshots__/util.spec.ts.snap

lib/platform/azure/index.spec.ts

lib/platform/azure/index.ts

lib/platform/azure/util.ts

...latform/bitbucket-server/__snapshots__/index.spec.ts.snap

lib/platform/bitbucket-server/index.spec.ts

lib/platform/bitbucket-server/index.ts

lib/platform/bitbucket-server/utils.ts

lib/platform/bitbucket/__snapshots__/index.spec.ts.snap

lib/platform/bitbucket/index.spec.ts

lib/platform/bitbucket/index.ts

lib/platform/bitbucket/utils.ts

lib/platform/common.ts

lib/platform/gitea/__snapshots__/index.spec.ts.snap

lib/platform/gitea/index.spec.ts

lib/platform/gitea/index.ts

lib/platform/github/__snapshots__/index.spec.ts.snap

lib/platform/github/index.spec.ts

lib/platform/github/index.ts