Expose `TeamsMessage` interface to support mocking #125

Job	Run time
Go Module Validation / Assert PR branch is ahead	16s
Dependency Updates / Assert PR branch is ahead	10s
Lint / Assert PR branch is ahead	6s
Vulnerability / Assert PR branch is ahead	5s
Vulnerability / govulncheck	17s
Lint / Lint Dockerfiles	6s
Lint / Lint Markdown files	7s
Dependency Updates / Look for available minor or patch releases	17s
Go Module Validation / Look for missing vendored dependencies	20s
Go Module Validation / Look for missing go.mod changes	12s
	1m 56s

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