Kill the surviving mutants in graph-source-github-issues #62

The GraphQL response guards, the rate-limit header parsing and the filter-to-variables and cursor encoding survive changes that break them. These are the most-affected files in @exadev/process-graph-source-github-issues on main's mutation run (https://github.com/ExaDev/process-graph/actions/runs/38170535483), with a few of the lines a surviving or uncovered mutant changes; the shard log and the uploaded HTML report have the full list.

packages/adapters/graph/source-github-issues/src/graphql.ts (31 survived, 6 without coverage):

• packages/adapters/graph/source-github-issues/src/graphql.ts:62:3 ConditionalExpression mutant, survived, on typeof value === "object" && value !== null && !Array.isArray(value);
• packages/adapters/graph/source-github-issues/src/graphql.ts:90:25 Regex mutant, survived, on if (reset !== null && /^\d+$/u.test(reset)) {
• packages/adapters/graph/source-github-issues/src/graphql.ts:94:7 ConditionalExpression mutant, survived, on if (retryAfter !== null && /^\d+$/u.test(retryAfter)) {
• packages/adapters/graph/source-github-issues/src/graphql.ts:123:5 ConditionalExpression mutant, survived, on response.status === forbidden &&

packages/adapters/graph/source-github-issues/src/source.ts (27 survived, 3 without coverage):

• packages/adapters/graph/source-github-issues/src/source.ts:85:42 ObjectLiteral mutant, survived, on ): Readonly<Record<string, unknown>> => ({
• packages/adapters/graph/source-github-issues/src/source.ts:87:5 ArrowFunction mutant, survived, on (state) => issueStates[state],
• packages/adapters/graph/source-github-issues/src/source.ts:89:11 LogicalOperator mutant, survived, on labels: filter?.labels ?? null,
• packages/adapters/graph/source-github-issues/src/source.ts:92:9 ObjectLiteral mutant, survived, on ? {

packages/adapters/graph/source-github-issues/src/cursor.ts (23 survived, 1 without coverage):

• packages/adapters/graph/source-github-issues/src/cursor.ts:122:9 ArrayDeclaration mutant, survived, on : [
• packages/adapters/graph/source-github-issues/src/cursor.ts:123:11 LogicalOperator mutant, survived, on filter.states ?? null,
• packages/adapters/graph/source-github-issues/src/cursor.ts:124:11 LogicalOperator mutant, survived, on filter.labels ?? null,
• packages/adapters/graph/source-github-issues/src/cursor.ts:127:15 ArrayDeclaration mutant, survived, on : [filter.order.field, filter.order.direction],

Kill them by asserting the behaviour, not by loosening or removing any existing assertion. Raise the package's breakThreshold from the new baseline once they are killed. Found while setting the break thresholds in #60.