🔨 Reduced the R CMD check coverage

* On Windows and macOS the checks are done according to CRAN: r-devel, r-release and r-oldrel. If you chose to have software that is older than a year - well, then its on you to make it work.
* On Linux: r-devel through r-oldrel-3 are tested with default compilers. If it is broken on Linux its most likely broken on MacOS and Windows too. So that will be the baseline.

Author: serkor1

.github/workflows/R-CMD-check.yaml

@@ -26,29 +26,23 @@ jobs:
           - {os: ubuntu-latest,   r: 'release',   compiler: 'default'}
           - {os: ubuntu-latest,   r: 'oldrel-1',  compiler: 'default'}
           - {os: ubuntu-latest,   r: 'oldrel-2',  compiler: 'default'}
-          - {os: ubuntu-latest,   r: '4.1.0',     compiler: 'default'}
+          - {os: ubuntu-latest,   r: 'oldrel-3',  compiler: 'default'}
 
           # Windows
           - {os: windows-latest,  r: 'devel',     compiler: 'default'}
           - {os: windows-latest,  r: 'release',   compiler: 'default'}
           - {os: windows-latest,  r: 'oldrel-1',  compiler: 'default'}
-          - {os: windows-latest,  r: 'oldrel-2',  compiler: 'default'}
-          - {os: windows-latest,  r: '4.1.0',     compiler: 'default'}
 
 
           # macOS Clang
           - {os: macos-latest,    r: 'devel',     compiler: 'clang'}
           - {os: macos-latest,    r: 'release',   compiler: 'clang'}
           - {os: macos-latest,    r: 'oldrel-1',  compiler: 'clang'}
-          - {os: macos-latest,    r: 'oldrel-2',  compiler: 'clang'}
-          - {os: macos-latest,    r: '4.1.0',     compiler: 'clang'}
 
           # macOS GCC via Homebrew
           - {os: macos-latest,    r: 'devel',     compiler: 'gcc'}
           - {os: macos-latest,    r: 'release',   compiler: 'gcc'}
           - {os: macos-latest,    r: 'oldrel-1',  compiler: 'gcc'}
-          - {os: macos-latest,    r: 'oldrel-2',  compiler: 'gcc'}
-          - {os: macos-latest,    r: '4.1.0',     compiler: 'gcc'}
 
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}