chore: Update dependabot labelling config (#5664)
chore: Update dependabot labelling config (#5664)

Label all dependabot PRs as "PR: dependencies", following
@rachel-fenichel's recent rationalisation of issue/PR labels.
google/blockly,google/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,mark-friedman/blockly,mark-friedman/blockly,mark-friedman/blockly,google/blockly,mark-friedman/blockly,rachel-fenichel/blockly,mark-friedman/blockly,google/blockly,google/blockly,rachel-fenichel/blockly,google/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,google/blockly,mark-friedman/blockly