Update api-spec.md to fix some formatting

[R2wenD2]

Removes stray text below WorkspaceDeclaration that has been included in the table.

Changes

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[R2wenD2]

/retest

[tekton-robot]

@R2wenD2: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-tekton-pipeline-alpha-integration-tests	b1fe9b4	link	/test pull-tekton-pipeline-alpha-integration-tests

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[imjasonh]

/lgtm

Whoops!

[bobcatfish]

/retest