Correct SHACL-SPARQL syntax of value selector

[ajnelson-nist]

This Pull Request resolves all requirements of Issue #499 .

Coordination

• [x] Pull Request is against correct branch
• [x] Pull Request is initially in Draft status
• [x] CI passes in UCO feature branch
• [x] CI passes in UCO current unstable branch (ffa5f3b)
• [x] CI passes in CASE current unstable branch tracking UCO's unstable as submodule (a6ec255)
• [x] Impact on SHACL validation reviewed for CASE-Examples
• [x] Impact on SHACL validation remediated for CASE-Examples (N/A)
• [x] Impact on SHACL validation reviewed for casework.github.io
• [x] Impact on SHACL validation remediated for casework.github.io (N/A)
• [x] Milestone linked
• [x] Solutions Approval vote logged on corresponding Issue (N/A)