Drop 4.1.1.pre.1 from rbs matrix

No prerelease newer than 4.1.1 exists yet (4.1.1.dev.1 and
4.1.1.pre.1 both predate the 4.1.1 stable release), so pinning to it
added no forward coverage over testing 4.1.1 itself.

Author: apiology

.github/workflows/rspec.yml

@@ -25,14 +25,12 @@ jobs:
         #   It currently 404s ("Unavailable version head for ruby"), failing CI:
         #   https://github.com/castwide/solargraph/actions/runs/25863741955/job/76000137015?pr=1187
         ruby-version: ['3.1', '3.2', '3.3', '3.4', '4.0']
-        rbs-version: ['3.10.0', '4.0.3', '4.1.1', '4.1.1.pre.1']
+        rbs-version: ['3.10.0', '4.0.3', '4.1.1']
         exclude:
           - ruby-version: '3.1'
             rbs-version: '4.0.3'
           - ruby-version: '3.1'
             rbs-version: '4.1.1'
-          - ruby-version: '3.1'
-            rbs-version: '4.1.1.pre.1'
     steps:
     - uses: actions/checkout@v3
     - name: Set up Ruby