[preset] Add sourcekit-lsp to swiftpm PR presets

In anticipation of moving sourcekit-lsp to build with swiftpm master
without using a Package.resolved pin, add sourcekit-lsp to the PR tests
for swiftpm.

Author: benlangmuir

utils/build-presets.ini

@@ -1380,6 +1380,12 @@ assertions
 llbuild
 swiftpm
 
+sourcekit-lsp
+
+install-swift
+install-llbuild
+install-swiftpm
+
 dash-dash
 
 skip-test-swift
@@ -1405,6 +1411,11 @@ xctest
 foundation
 libdispatch
 llbuild
+sourcekit-lsp
+
+install-swift
+install-llbuild
+install-swiftpm
 
 skip-test-swift
 skip-test-cmark