fix(ci): bump R version 4.4 → 4.5 for Boom >= 0.9.16 compatibility

Boom 0.9.16 (2025-09-02) requires R >= 4.5.0.
R 4.4 causes "dependencies 'bsts', 'Boom' are not available" error
because CRAN filters out incompatible package versions.

Author: YuminosukeSato

.github/workflows/numerical-equivalence.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: r-lib/actions/setup-r@v2
         with:
-          r-version: "4.4"
+          r-version: "4.5"
       - name: Install R packages
         run: |
           Rscript -e "install.packages(
@@ -50,7 +50,7 @@ jobs:
           token: ${{ secrets.GITHUB_TOKEN }}
       - uses: r-lib/actions/setup-r@v2
         with:
-          r-version: "4.4"
+          r-version: "4.5"
       - name: Install R packages
         run: |
           Rscript -e "install.packages(