Add a test for runtime.txt with full R version specified

Catching possible errors as reported in https://discourse.jupyter.org/t/error-in-mybinder-org-there-is-no-package-called-irkernel/32478/13.

The other tests only specify x.y, not x.y.z

tests/r/r4.3.2-rspm/install.R

@@ -0,0 +1 @@
+install.packages("digest")

tests/r/r4.3.2-rspm/runtime.txt

@@ -0,0 +1 @@
+r-4.3.2-2024-01-10

tests/r/r4.3.2-rspm/verify

@@ -0,0 +1,13 @@
+#!/usr/bin/env Rscript
+library('digest')
+
+# Fail if version is not 4.3
+print(version)
+if (!(version$major == "4" && version$minor == "3")) {
+  quit("yes", 1)
+}
+
+# The date we have chosen should give us an rspm mirror
+if (!(startsWith(options()$repos["CRAN"], "https://packagemanager.posit.co"))) {
+  quit("yes", 1)
+}