Drop testing for "lowest" dependencies in PHP 8.0 upgrade (#161)

As per composer/composer#9302, this is a known composer bug
that is not that relevant for this package for multiple reasons:

 1. the only real dependencies are `php` and `composer-runtime-api`, which are fixed
 2. we upgrade all dependencies whenever possible, and restrict the range too, via
    dependabot, so we don't keep old dependencies around for too long anyway

.github/workflows/coding-standards.yml

@@ -48,10 +48,6 @@ jobs:
           key: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
           restore-keys: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
 
-      - name: "Install lowest dependencies"
-        if: ${{ matrix.dependencies == 'lowest' }}
-        run: "composer update --prefer-lowest --no-interaction --no-progress --no-suggest --ignore-platform-req=php"
-
       - name: "Install highest dependencies"
         if: ${{ matrix.dependencies == 'highest' }}
         run: "composer update --no-interaction --no-progress --no-suggest --ignore-platform-req=php"

.github/workflows/mutation-tests.yml

@@ -50,10 +50,6 @@ jobs:
           key: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
           restore-keys: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
 
-      - name: "Install lowest dependencies"
-        if: ${{ matrix.dependencies == 'lowest' }}
-        run: "composer update --prefer-lowest --no-interaction --no-progress --no-suggest --ignore-platform-req=php"
-
       - name: "Install highest dependencies"
         if: ${{ matrix.dependencies == 'highest' }}
         run: "composer update --no-interaction --no-progress --no-suggest --ignore-platform-req=php"

.github/workflows/phpunit.yml

@@ -17,7 +17,6 @@ jobs:
     strategy:
       matrix:
         dependencies:
-          - "lowest"
           - "highest"
           - "locked"
           - "classmap-authoritative"
@@ -54,10 +53,6 @@ jobs:
           key: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
           restore-keys: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
 
-      - name: "Install lowest dependencies"
-        if: ${{ matrix.dependencies == 'lowest' }}
-        run: "composer update --prefer-lowest --no-interaction --no-progress --no-suggest --ignore-platform-req=php"
-
       - name: "Install highest dependencies"
         if: ${{ matrix.dependencies == 'highest' }}
         run: "composer update --no-interaction --no-progress --no-suggest --ignore-platform-req=php"

.github/workflows/psalm.yml

@@ -50,10 +50,6 @@ jobs:
           key: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
           restore-keys: "php-${{ matrix.php-version }}-${{ matrix.dependencies }}"
 
-      - name: "Install lowest dependencies"
-        if: ${{ matrix.dependencies == 'lowest' }}
-        run: "composer update --prefer-lowest --no-interaction --no-progress --no-suggest --ignore-platform-req=php"
-
       - name: "Install highest dependencies"
         if: ${{ matrix.dependencies == 'highest' }}
         run: "composer update --no-interaction --no-progress --no-suggest --ignore-platform-req=php"