feat: bump minimum supported PHP to 8.1 #59

Job	Run time
Generate job matrix	5s
QA Checks (README Linting [8.1, locked], ubuntu-latest, laminas/laminas-continuous-integration-ac...	20s
QA Checks (PHPUnit [8.1, locked], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	20s
QA Checks (PHPUnit [8.1, lowest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	22s
QA Checks (PHPUnit [8.1, latest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	27s
QA Checks (PHPUnit [8.2, lowest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	23s
QA Checks (PHPUnit [8.2, latest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	22s
QA Checks (PHPUnit [8.3, lowest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	23s
QA Checks (PHPUnit [8.3, latest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	20s
QA Checks (PHPUnit [8.4, lowest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	19s
QA Checks (PHPUnit [8.4, latest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	25s
QA Checks (PHPCodeSniffer [8.1, locked], ubuntu-latest, laminas/laminas-continuous-integration-ac...	22s
	4m 8s

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