Bump minimum supported version to 5.10

Some fundamental modules only support 5.10, for example:
FAIL CPAN-Meta-Requirements-2.143 requires perl v5.10.0, but you have only 5.008009

.github/workflows/publish-to-docker.yml

@@ -20,7 +20,7 @@ jobs:
         id: action
         uses: perl-actions/perl-versions@main
         with:
-          since-perl: '5.8'
+          since-perl: '5.10'
           with-devel: 'true'
 
   # bookworm base images only exist for 5.36 and newer.
@@ -76,7 +76,7 @@ jobs:
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_GITHUB_TOKEN }}
           dockerfile: Dockerfile
-          buildargs: BASE=${{ matrix.perl-version }}-buster,CPANOUTDATED=${{ matrix.perl-version != '5.8' }}
+          buildargs: BASE=${{ matrix.perl-version }}-buster,CPANOUTDATED=1
           tags: "${{ matrix.perl-version }}-buster,${{ matrix.perl-version }}"
 
   build-bookworm:
@@ -98,5 +98,5 @@ jobs:
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_GITHUB_TOKEN }}
           dockerfile: Dockerfile
-          buildargs: BASE=${{ matrix.perl-version }}-bookworm,CPANOUTDATED=${{ matrix.perl-version != '5.8' }}
+          buildargs: BASE=${{ matrix.perl-version }}-bookworm,CPANOUTDATED=1
           tags: "${{ matrix.perl-version }}-bookworm"

.github/workflows/test-cpanfile.yml

@@ -17,7 +17,7 @@ jobs:
         id: action
         uses: perl-actions/perl-versions@main
         with:
-          since-perl: '5.8'
+          since-perl: '5.10'
           with-devel: 'true'
 
   test-job:

README.md

@@ -95,7 +95,6 @@ devel
 5.14
 5.12
 5.10
-5.8
 ```
 
 ## devel build
@@ -112,7 +111,7 @@ versions without an explicit Debian version are `buster`.
 
 ## Using the images with GitHub Workflow
 
-Here is a sample workflow for Linux running on all Perl version 5.8 to 5.38
+Here is a sample workflow for Linux running on all Perl version 5.10 to 5.38
 You can save the content in `.github/workflow/linux.yml`.
 
 Note: this example is using cpm to install the dependencies from a cpanfile.
@@ -159,7 +158,6 @@ jobs:
           - '5.14'
           - '5.12'
           - '5.10'
-          - '5.8'
 
     container:
       image: perldocker/perl-tester:${{ matrix.perl-version }}